They do have to be different colour changes since if your tamagotchi is yellow, it wont change colour from more lemon pies since it is already yellow. Another thing to note is that it seems if the parent of your current genetics mix has a colour that is identical to a colour change effect, it will need to change into two different colours from its parent to unlock the salon. What happened to me is that my first On was actually a Mametchi who was turned orange by eating rice omelets/omurice. He married a Lovelitchi and the offspring turned pale yellow, the same colour that results from eating lemon pies. This colour was passed down that when I tried to unlock the salon, I had to change my tamas colour three times since I first "changed" it to yellow, then to orange, and finally white. While my tama was orange, it wouldn't unlock but only when I made her white. There is another possibility that perhaps they have to change two different colours in one day.