There are certain foods the turn your Tamagotchi M!x different. Before adult they go away with evolution, but at adult they're permanent. Sorry. But they DO affect the colors of future generations, so you can m!x the colors of tamas too.
Lemon Mousse turns then yellow (Restaurant)
Tomato Juice turns them red (Restaurant)
Melon Soda turns them green (Restaurant)
Neapolitan turns them orange (Restaurant)
Honey Rose Tea turns them pink (Flower Hills)
Marine Juice turns them blue (Mermaid Palace)
Squid Ink Pasta turns them black (Mermaid Palace)
Cotton Candy turns them white (Rainbow Hills)
Sweet Potato Jelly turns them purple (Gozaru Hills)
Shinobi Sesame Pudding tuns them gray (Gozaru Hills)
and Lemonade also turns them yellow (Melody Land)