Totally agree with @keith_thompson on this. Ran into the same problem with a traffic light system on a report. Swapped to check, dash, and X for good, okay, and bad. The number of support tickets about it dropped to zero overnight. You really have to assume someone using your stuff can't see color differences. Icons with distinct shapes are just way more reliable than color alone.
Feel that so hard! I once tried to use blue and purple dots to mark different tasks on a family calendar. My husband could not tell them apart at all, it was a mess. Switched to stars and circles and suddenly the whole system worked. It's wild how such a tiny change can make things clear for everyone.