The markings will show more and stay consistent. Of course a bright red garnet is ideal. Anything of red will do this. I've tried 5-6 combinations.
it does take some getting use to on the eyes cuz it's a lot of red, but I'm a firm believer with my own substrate experimenting. That when their markings are showing often. Therefore, have a potential to be much more active and swim around. But this just me I guess.