It seems to me that the solution to increasing the numbers' readability is simply using colours that contrast each other in hue rather than sit adjacent on a ramp.
For example, in the Windows version of Minesweeper on my computer, 1=blue, 2=green, 3=red, 4=indigo, 5=burgundy, 6=blue-green...
In the average game, 1 is the most common, with 2 and 3 making up the majority of the rest of the numbers on the screen. Shouldn't these three numbers have hues that are the farthest distance apart for readability purposes? Rarely seeing a 5 or 6, and almost never a 7 or 8, the "ramp" theme, though in theory unifying, might not be nearly as apparent to players as you'd like. The saturation increase was a step in the right direction, but doesn't remedy the readability problem, because at a glance, 1 and 2 simply need to look quite different.
