Lovely additions, Graeme! I particularly like this species. They have remarkable colour change capacity depending on what they are resting on. Very quick to grab frozen food too - do as Jim suggests but don't blink or you'll miss it!
I think we had a discussion on this a year or so ago, but didn't come up with anything definite. Some specimens have a lot of red colouration in the pectoral, pelvic, and even the caudal fin, plus red tubercles. I'm not sure if any direct comparisons were made with body shape vs. colouration etc.