The colors we were using (gray for unpressed buttons and green or red
for pressed buttons) didn't contrast well against a white background, so
we're now using darker colors.
However, with darker colors, using solid icons for the unpressed buttons
makes it harder to differentiate when a button is pressed and when it
isn't, particularly for color-blind people.
So we're now using regular icons for the unpressed buttons and solid
icons for the pressed ones.
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