Big thank you for the kind words (seeing bad reviews on other sites kind of dims the desire to continue working on any project, yet these are quite inspirational T^T ).
The side games are meant as somewhat of a side stories (Kingdom Hearts like..well kind of), hopefully enriching the SB universe.
"fapets with a unique version" : as @CrowNoRi pointed out, these are most likely be in special events or time-location limited to get a more rare sensation. There are some different bunnies in winter/xmas area (bright colored hair + light shimmers come from their hair), yet they have a rare drop/spawn. Btw, 'the rainbow hair bunny' did you had in mind the 2 young bunnies from the Bunny lair (story) ?
P.S.: Feel free to rate the game (if it still hasn't been done yet) and recommend to others ^.^