The number 4 is too similar-looking to the number 1 - I've blown up because I thought there was only 1 TNT, only to squint afterwards and be like "oh wait, that was a 4"
I set the 1 to be white so it looks the most neutral and made 4 cyan and 5 yellow. I switched to the skinnier font and dropped the transparency to level 4 of 5. That stopped all the hard to read number problems.
But agreed, that dark blue 4 is no good. The darker colors in general don’t work that well.