What are the ways that color blind people figure out that they're color blind?

Testing: The most common type of "color blindness" is red-green color deficiency. Blue-yellow deficiency or true color blindness (achromatopsia) are rare. Color testing can identify which. The problem is a lack of certain types of cones or their opsins (light-sensitive compounds). Red-green deficiency can be adapted to fairly easily and is not very limiting, but the others can significantly impact vision.

Testing/comparison: Color deficient children usually do not know about it since they have no internal standard of comparison. Many find out about it upon entering school when color matching in the courses or in play provides them a look at the differences. Others don't know about it until testing later in life for jobs, or screening such as in the military. Many never find this out and usually function well.