This feature of the game is currently Unreleased. There may be changes in the future that will affect the development of certain features of the game.
The Secret Style Pack is an upcoming paid cosmetic DLC pack which will change slime appearences between its standard appearence, and a new cosmetic one. Largos can be tweaked between both its slime variants.
- http://www.slimerancher.com/SecretStyle/ - Announcement of the DLC in detail.