How to choose colors for your CLI applications (2023)
(blog.xoria.org)186 points by kruuuder 3 days ago
186 points by kruuuder 3 days ago
> refrain from setting background colors
That's the thing though, setting bg color opens up a lot of options, and constraining to invert is not sufficient in my opinion.
Sticking to the \x1b[4X background color is probably safe as that can be tweaked by terminal color palettes. It’s when you use the 256 or RGB \x1b codes that it becomes an issue. Ok for foreground.
That’s fine, but please make the colors configurable then.
For example like Mutt does: http://www.mutt.org/doc/manual/#color
> constraining to invert is not sufficient in my opinion
Eh. Doing green/red text color with default background, maybe inverted works amazing for me. In fact, I'd say that every sensible colour scheme for a terminal should have as the default foreground/background colours something that is more or less contrasting against every other explicitly named colour, including black and white (I personally have #212121 on #EEEEEE).
Use only default (white/black), red for bad, green for good. If you need more than that, like vim or whatever, then maybe a 'fullscreen' TUI is better, with a specified background and foreground. For CLI tools, I'm not sure if I prefer more colours.
The CSS to make the terminals look like iTerm was smooth, to the point I read them as screenshots.
> red for bad, green for good
8% of men of Northern European descent (and 0.4% of women) are red-green colorblind. That'd be a terrible choice. Use blue-orange, blue-red, or purple-green.
This approach is worse. Use red and green like everyone else and the user can choose their terminal color palette to differentiate in a way that works for them. Then it works the same across all commands. If you're the odd one out, you're adding more mental overhead for the user, not less.
Red/green has no inherent semantics. It has the semantics that you assign it. If you choose to assign it meaning that disenfranchises 8% of men using your system, that's your choice, but it is not a good one.
Emojis aren't 7-bit clean. They're hard to type. They don't mean things the same way words do. `foo | grep -i error` communicates intent better than `foo | grep :-/` or whatever goofy hieroglyph someone chose instead of, like, a word with clearly defined meaning.
Context here matters, red finds its way into Chinese forbidden or warning signs quite often.
Eh, LS_COLORS is sometimes useful once the meanings are in your subconscious.
A confused user once stopped by, they had a blank terminal, so I showed them how to select all which revealed the helpfully black on black text. These days I compile colour support out of st, or set *colorMode:false for xterm. "But you can customize the colours" is a typical response, to which one might respond that one has grown weary of pushing that particular rock, and moreover one may be busy with other things at a drag-out monitor in a server room at three in the morning that has helpfully dark blue text on a black console, or worse if some high-minded expert has gone and rubbed the backside of a unicorn everywhere so that they may improve the "legibility".
Colourful terminals are so useful. I have mine colour coded according to the working directory depending on the project. So I can see which terminal is associated with which project even if there are twenty terminals open. The scripts are even in my servers so when I ssh in to them it changes colour as well.
As long as you respect the NO_COLOR variable, it will work for me.
There's an ever more basic rule: don't just make your text white (ANSI 37m) because you assume the terminal will have a dark background. Even white-on-black (37;40m), while usually readable, can stand out the wrong way if you assume that everyone is using dark mode.
IMO if your terminal theme does not provide high contrast for "white" text on the default or "black" backgrounds, that's for you to fix. If you want a light terminal then change the color scheme to map "black" to a bright color and "white" to a dark color while making sure that other colors have good contrast to your "black". Don't just change the default foreground and background color and expect every single color using program to fix your mess.
I made the "Aardvark Blue" a while back[1] to solve some of the problems that most color schemes have. The goal of this theme is that:
- colors are fairly natural
- background and black are distinct
- grays are naturally ordered avoiding full black
- light and dark colors are distinct from each other
- all colors look good on background, black, dark gray, gray, white
We use this for all the screenshots on https://ratatui.rs and https://github.com/ratatui/ratatui
It's available from the usual places https://iterm2colorschemes.com/, https://windowsterminalthemes.dev/?theme=Aardvark%20Blue, built in to ghostty, extension for vscode etc.
[1]: https://github.com/mbadolato/iTerm2-Color-Schemes/pull/417
iterm2colorschemes is a source for various other tools as it ports out to
"Terminal, Konsole, PuTTY, Xresources, XRDB, Remmina, Termite, XFCE, Tilda, FreeBSD VT, Terminator, Kitty, MobaXterm, LXTerminal, Microsoft's Windows Terminal, Visual Studio, Alacritty, Ghostty, and many more."
You may have used data from it without knowing about it.
Yeah, when I created that repo, it was for me to store iterm themes that I found, and it took off and got ports to, well, pretty much every terminal . I didn't want to rename the repo since it's linked to in so many places. The main link people usually see is iterm2colorschemes.com but I do own terminalthemes.com and should probably just get around to pointing that one to the repo, too
I don't usually look anywhere, but things I sometimes see pop up in various places are eg https://terminal.sexy/ or https://vimcolorschemes.com/
The problem with CLI colors is that they operate on the wrong abstraction layer. Individual program shouldn't send "this text is red" but "this text signals failure" and then terminal interprets "failure" as "red". Until this change happens (never) colors in CLI will remain a hot mess.
I really think we should converge to semantic codes. By example Background is zero, standard is 7, positive / negative, highlight, colored1,2,3 .. with correct defaults, and let the user have a common 8 or 16 colors palette in the terminal for all textmode apps. Imagine having some kind of unified color themes in the terminal.
I’ve bounced off of LazyGit multiple times because I never figured out how to make it play nice with a light theme terminal.
I haven’t used dark mode anything for years. I set my monitor so it’s roughly as bright, or slightly brighter than, a piece of white paper.
No more flash-bangs when some website doesn’t support dark mode.
Xterm is actually a terminal emulator, and has to pass a suite of conformance tests that actually check its emulation of DEC VT series terminals.
Most of its successors are more like "shitty xterm emulators" whose conformance tests are "do my favorite mOdErN CLI apps work".
I agree. So many TUIs from webshit devs don't even bother to call isatty, let alone check terminfo to see if ANSI escape codes are even valid for this terminal.
But modern open source subscribes to Mao's Continuous Revolution Theory. Calls for some measure of stability and sanity are usually dismissed with some form of the argument "awwww, is poor diddums afwaid of a widdle change?" Or in this case, "still using vi on your ADM3A, old timer? Our software is not for you."
Emacs on a Link MC5, although something doesn't like how the terminal handles flow control. I'm not sure if it's the O/S, the UART, the cable, or the terminal, but I have issues with I/O corruption. Even something a simple as a directory listing will get messed up, and on both FreeBSD and Linux, so maybe that rules out the O/S. Oh well. I'll figure it out some day.
I recently spent several evenings re-working all of my colours across all of my computers and screens; terminals, IDEs, etc. Ultimately, despite using the same tools, and always dark mode, across all of my machines, the setup for each was different.
I think it's safe to set a standard colour-set so that it's immediately usable, but beyond that, a user should be customising to their requirements.
Perception differs among people; many of the colours OP listed as unreadable, were barely an issue, bright yellow being the only one I could unequivocally agree on. Perhaps display type, configuration and colour calibration is an important factor, as well as individual perception, ambient conditions, brightness levels, contrast, and perhaps even more variables have a significant effect.
I've also learned, since adding an OLED Monitor to my desk alongside the IPS ones, that it's possible to have too much contrast; brightly coloured text alongside pixels that are literally off can be just as problematic to read at times, as low-contrast.
If you want a quick easy way to add some colors to your own shell scripts:
export STDOUT_COLOR_START='[34m'
export STDOUT_COLOR_STOP='[0m'
export STDERR_COLOR_START='[31m'
export STDERR_COLOR_STOP='[0m'
print_stdout() {
printf %s%s%s\\n "${STDOUT_COLOR_START:-}" "$*" "${STDOUT_COLOR_STOP:-}"
}
print_stderr() {
>&2 printf %s%s%s\\n "${STDERR_COLOR_START:-}" "$*" "${STDERR_COLOR_STOP:-}"
}
The source also has functions for nocolor, and detecting a dumb terminal setup that doesn't use colors, etc.
That seems needlessly cumbersome, why not
declare STDOUT_COLOR='\e[34m'
declare STDERR_COLOR='\e[31m'
declare COLOR_STOP='\e[0m'
print_stdout() {
echo -e "${STDOUT_COLOR}${*}${COLOR_STOP}" &> /dev/stdout
}
print_stderrr() {
echo -e "${STDERR_COLOR}${*}${COLOR_STOP}" &> /dev/stderr
}
And those print statements aren't going to work by default.
Interesting analysis, but perhaps it warrants a different conclusion: it's almost impossible to please everyone in this case. The resulting colours seem of some utility, but if you intend to make something more interesting you're probably annoy some (potentially large) group, in the case of legacy terminal coloring.
I used solarized since it came out but I dropped it some years back. I don’t think I can use it for dark mode. It’s too washed out and dull compared to light mode which is what I used to use it with. I just use whatever VS Code or VIM gives me as a dark mode and it’s usually better.
Black on white has seemed to work for centuries without issue. For general reading, throw in bold and italic and you're pretty much set. For programming, black on white is still a go to color (or lack thereof).
If the goal of the post is to pick terminal colors that contrast on both white/light and black/dark backgrounds, it means you're stuck with midtone colors (between light and dark). This is really limiting for color choice (there's no such thing as "dark yellow" for example), and lowers the maximum contrast you can have for text because you get the best contrast when one color is dark and the other is light.
Ideally, instead of the CLI app switching to "bright green", it would pick a "bright contrasting green". So if the terminal background was dark, it would pick bright green, and for light background it would pick a darker green. There isn't CLI app implementations for this? This is similar to how you'd implement dark mode in a web app.
> Ideally, instead of the CLI app switching to "bright green", it would pick a "bright contrasting green". So if the terminal background was dark, it would pick bright green, and for light background it would pick a darker green. There isn't CLI app implementations for this? This is similar to how you'd implement dark mode in a web app.
The responsibility for this lies with the color scheme not the terminal program.
CLI apps can detect the background color of the terminal, and determine contrasting colors accordingly.
It's not recent, and most terminals support it. You send an escape sequence to the terminal, and get back a sequence that tells you the exact background color.
Huh, indeed. I still can't find much information about this, but this page is very informative: https://jwodder.github.io/kbits/posts/term-fgbg/
Here is a screenshot for my personal example:
https://github.com/workglow-dev/workglow/blob/main/docs/deve...
Play with it here using dev tools (you can ignore the website itself): https://workglow-web.netlify.app/
Docs including útil for checking dark mode: https://github.com/workglow-dev/workglow/tree/main/packages/...
I use the built-in TokyoNight Day theme as my light theme in GhosTTY and I think it's almost perfect. Then I use TokyoNightMoon for dark. Works great. Hard to use anything else now.
If you're CLI application doesn't play nice with it (i haven't seen many) I don't use it.
It's easier to see dark text on a light background for people with astigmatism.
Or for people working outside. Or for people using an e-ink display.
Accommodating terminal colour schemes, however crazy to you they might be—white on black, black on white, dark brown on off-white Solarized-style, etc.—is basics of TUI design.
Personally I alternate between light on dark and dark on light (the latter sometimes together with OS-wide colour inversion feature).
> People who use white themed terminals are psychopaths anyway
Dark background is hell for anyone with astigmatism. It’s fine with 80x24 (vga text mode), but for anything higher feels like light needles on the retina. With astigmatism everything that is bright and small is duplicated, which means small characters is very difficult to read.
Can you work this into an AGENTS.md ? Just so happen to be working on multiple TUI at the moment: text-based modern web browser, VPS rental console, agentic coding wrapper.
Colors, have been a perpetual nightmare.
As long as CLI programs stick to the 8 or 16 standard colors and refrain from setting background colors (inverse mode is fine), as well as from explicitly setting white or black as text color, everyone can reasonably configure their terminal colors so that everything is readable.
When going beyond that, the colors really need to be configurable on the application.