Comment by econ

Back when systeem colors were actually cool I made some system color styles. It looked really nice but you don't know how they contrast. That one is called [say] buttonFace and another buttonText turned out to to be meaningless. Someone wrote some js for me that took getComputedStyle and calculated the contrast. If it was unacceptable it either took a second candidate color or failed back on text-shadow to darken or lighten an aura around the text sufficiently.

https://i.sstatic.net/18bQt.png

I forget the calculation but thinking about it you can probably just take the average of the 3 rgb values and compare them(?) It would produce a low value for blue and give preference to white text.