Here’s an example of mapping where having two very similar shades (at least to my eyes) doesn’t help me an awful lot.
This is an Optus map of 3GSM coverage in South Australia. There is no facility to zoom into the map for greater detail, so my eyes are at the mercy of Optus’ no doubt superbly sighted graphic design department.
I’m red and green colour-blind (as a lot of men are), so brown shades are tricky for me to distinguish from each other. Sigh.