That little picture beside my name is my male at 3 months. That was one of the reasons I selected him. I have always just taken it as a sign of good health. I have seen some males take six months. My female never showed any real colors tell she was near a year old and about to bust with eggs.
Just like Will said, there are many variables. There are many pics out there showing growth patterns and various coloration. Here is a link to my gallery with pics of my 6-7 month ambiobe panther. It seems with every day his blues and greens are getting richer. https://www.chameleonforums.com/gallery/browseimages.php?c=3&userid=822