In this day and age pretty much the only thing I find need to print is patterns for sewing, knitting, and crochet. Sometimes different sizes or different instructions (like, blue means do this, while yellow means do that) is only differentiated by different colors. Often colorwork charts with more than two colors indicate where the colors go using only different colors (up until maybe the 90s it was common to use symbols instead, and some designers still do, but it's pretty common for modern charts to just use color). Sometimes even with only two colors, the designer uses colors that are close enough together that printing it in black and white doesn't work.
Knitting and crochet patterns can be used digitally, and that's what I do most of the time, but that's not feasible with sewing patterns (well, some people can use a projector, but that doesn't really work for me) and even with knitting and crochet patterns it's sometimes easier or necessary to print them out. Like if I'm going to work on something while away from any desks - I'm trying to get out of the habit of balancing a phone or tablet on my leg, since I broke a phone screen (although it didn't happen while balancing it on my leg, I know that's a risk). Or if I'm working on a complicated chart, it's easier to visually isolate the row I'm working on - I sometimes do this using photoshop if I'm at my computer, but it's a pain to do it digitally anywhere else.
I imagine many other people lead lives where color printing is necessary...