I always thought that becoming an adult meant getting a matching set of towels for your household.
But unless you live alone, and especially if you entertain guests (such that you can’t rely on placement for identifying your towel), color is a simple way to avoid getting towels mixed up.
I think it’s best to stick with the same type from the same brand, for background uniformity, but pick a handful of colors that you find pleasing together.
(It also gives a little excitement and variety to your linen closet and lets you have white or light colored towels as well as towels for that time of the month)