Button text should be white to improve legibility

[mattbirchler]

I'd like to propose changing the text color of buttons to white. The text is currently black, which I believe was selected because it's technically more contrast to the background colors, but I think the colors in question fall into the color range when the most contrast is actually less legible (read more here).

Here's a comparison of the current colors compared to this proposal.

[mattbirchler]

I'll add that changing the text to white isn't the only solution here. The color could be dynamic based on the background color chosen or maybe the accent colors could be changed to lighter variants that would make the current black text work better.