I got bored and made a spreadsheet of all the available pets and which colors they're available in (excluding Experiment pets). Here's a link to the file, in case anyone wants to check it out: pet color Excel spreadsheet The spreadsheet also includes stat totals for the different pet species and colors. Incidentally, the pet that comes in the least colors is the Scootle, and the color that the fewest pets come in is Harvest.

EDIT 1-22-2019: Updated the link with the new version. I also put a link on my profile. I'll make sure to keep the link on my profile updated, so if you click the link in this post and it doesn't work, check my profile for the newest version!