The AntsCanada Ant Forum's

Can you just use something like a non-toxic red sharpie or marker to color the acrylic of an ant nest to give them artificial darkness? It's really hard to find red cellophane here. I would assume as long as it makes the light red, the ants should feel at ease.

That would probably work if you can get it thick enough.

Well I don't think the fire ants will really care... but if the thief ant colony starts growing big enough first, they may be bothered by the light. However, I'm using purple/pink plant lights in that area so I'm not sure they'd care in the first place.