Which is great if you are fully abled! But for folks for whom sight isn't as strong, additional aids (different colors, different sized banknotes for different denominations) are super helpful.

Being fully sighted, I still appreciate it.

https://en.wikipedia.org/wiki/Curb_cut_effect

Some currencies also have braille-like embossments so that if you're totally blind, you can still pick out the correct denominations.