Now that color-changers have been fixed and no longer switch skins each time they're summoned, I'm in the process of replacing many pets and acquiring duplicates in some cases. But they can't be just any old quality. No, they must be rare!
This has proven quite the challenge due to my specific requirements. However, Wain from WarcraftPets posted a method for finding that perfect pet.
Rather than looking just for primaries of a specific color and hoping that they're rare, check all pets in the zone for secondary rares. If a second or third companion in the lineup are rare but not the color you're looking for, simply relog.
The pet and its team, as well as the qualities of each pet should be the same after you log back in. However, the skin of each secondary companion has the chance to change!
Note: Only the second and third pets have a chance to switch colors after relogging. The primary wild pet's color is fixed to the one it spawned in with.
With this information under my belt, collecting all the colors in rare quality is going to be much easier (hopefully)! I'll definitely be checking more pets for secondary rares now.