You can copyright just about anything as long as you have the _money_
T-Mobile trademarked a very specific pink, "Magenta"
There’s even a company that holds trademarks on a set of colors, Pantone.
Courts have yet to reverse or revoke these silly trademarks.
T-Mobile does not have a trademark on the color magenta, nor does Pantone on any colors.
The trademark is for using that color to market your product such that a buyer might assume they are buying T-mobile, but in reality they are not.
Or for Pantone, that a buyer is buying a color quality controlled by Pantone.
Trademark and copyright are not the same thing..