Umm, you mean first of its kind site-wide? As in, nobody else has had this colour yet?
That MIGHT work with some of the Throdama colourings, since they also have their morphs with different colour genes and they haven't been around that long, but all the other species have for sure been bred multiple times already in every possible colour. If you check under Help -> List of Skins, you can check how many colour possibilities for each species there are. Not that many. The game has been around for a while and many people have already tried for the rare colours.
If you mean first of its kind in your own stable? Sure, that's an interesting project - it's what I'm doing for myself. One of my goals is filling up my own Reserve with pets of every colour. Therefore I slowly breed my pets to the rare colours and as such have a first of its kind in my stables.