Hi paddone , I'd say that the different colours are definitely light oriented , I find the brightest bits , oranges , pinks mainly in quite dark areas of the tank , normally when I shift a rock etc . I think corraline growth and colour or sometimes lack of it could be due to excessive light . I've never really had much grow on the glass until recently which I think is the result of knocking back my lighting a bit . I now have a little growing on a couple of small areas on the base only . As far as my rock goes I also find better corraline coverage , mainly standard purple , on the rocks in not so bright areas of the tank .