I used some pure Astaxanthin for quite a while on some of my collareds and did not see anything noteworthy. I know in birds and fish, companies often boast that carotenoid containing foods will boost the colorations. My opinion is this does not carry over into reptiles. At least I did not see it.
I used pure Astaxanthin mixed with the food (shaken with crickets) and also used it to supplement the crickets diet. The crickets were gutloaded with big red bellies.
the variety I was using was being produced by a yeast. The asta was actually contained within the yeast cells.
Honestly I would not waste any money on supplementing the foods for colorenhancement. Natural lighting and good health, and the lizards gentics will make all the difference in the world.
John