Who is the visitor?

A black kitten appears intermittently in our garden and is very interested in the birds!! The puzzle is.... the visitor sometime has a blue collar, sometimes a pink one and at other times it doesn't have a collar. The question is..... is this a very fashion conscious kitty or are there 3 kittens? We never see more than one at a time and it is very timmid, so runs away as soon as we go out in to the garden.