Several colors, though I do tend to use one at a time until it runs out before switching. Whiteboard markers don't really work though (too transparent when it'

Several colors, though I do tend to use one at a time until it runs out before switching. Whiteboard markers don't really work though (too transparent when it's bright out). Permanent markers and liquid chalk work best, though the latter can be especially annoying to erase. Some glass-specific erasable markers aren't bad either.