One of my favorite things to do in Mono is to pick a single color and go from dark to light in that color. Say I picked red; when the track is slow, the bricks would be dark maroon, almost invisible against the black background, and when it's fast, the bricks would be light pink, almost white. I like this just for its aesthetic values, but stay a little farther from the extremes near black and white and this could be an effective way to work around colorblindness by sticking to a single color that isn't a problem to distinguish from grey. Of course then I have to change back to easily distinguishable colors to play Puzzle mode, but then I don't play Mono that often. I wish we could save custom color configurations.
(When I really want a mind-screw, I'll change the red, green, and purple blocks ALL to the same dark color, and the yellow and blue to something very light, so that as the track changes slope it very rapidly lights up and goes dark again. Not that good for gameplay and probably murder for the folks who are supposed to be scared off by the epilepsy warning. But it looks awesome.)