UPDATE#1 - REQUEST - Colorblind color-swap test.

[ianhamilton_]

Yes, it is possible to be completely red/green colour blind. Anything less is deficiency rather than blindness.

Justin, that contrast point is key. If you already have symbols to denote things the differences in colour between them aren't really important, what's important is being able to tell them from the background. An easy fix is make them relatively light, and give them a dark stroke or shadow. That makes them visible against both light and dark backgrounds. Particularly important bearing in mind red or green can appear to be a much darker shade.

[ianhamilton_]

Also have you thought about using animation? A symbol pulsating when it is damaged?