I have had 3 ocellaris clowns for almost a year now. When I bought them they were all about an inch long. Two of them have paired and hang out together all the time, while the other clown (an immature male) is allowed to hang out closely with them. The males have grown very slowly and have not changed color at all, while the female grew faster and is now quite a bit bigger.... as for colour, she has also darkened up a bit. Then again all my clowns are still young.
I wouldn't suggest getting more then 2 though as from what I have read most of the time more than a pair cause fighting.
Here is a recent picture of my clowns with my Bubble Tip Anemone... you can see the colour difference between the female and the males.
