Critic Ivor Smallbrain is watching the horror movie Salamanders on a Desert Island. In the film, there are 30 salamanders living on a desert island: 15 are red, 7 blue and 8 green. When two of a different colour meet, horrifyingly they both change into the third colour. (For example, if a red and a green meet, they both become blue.) When two of the same colour meet, they change into both of the other colours. (For example, if two reds meet, one becomes green and one becomes blue.) It is all quite terrifying.

In between being horrified and terrified, Ivor idly wonders whether it could ever happen that at some instant in the future, all of the salamanders would be red. Can you help him?