Do you feed a lot of shrimp or a red pellet? When i used to feed Nutrifin gammarus pellets (which are pink) i noticed a pinkish tinge around the scuts on the plastron. This faded after quiting that food.
I doubt that that is the issue unless you've just switched food. My actual first guess would be a skin infection. The pink colour would make me think the skin is irritated or inflamed. Is the skin bumpy, or swollen?
What parametres are you keeping them in, like tank size, lighting, food, etc.
If it is a skin infection, a trip to the vet would be the very best place to start.
-----
- Melanie
2.1.0 cats
3.3.5 crested geckos
0.0.4 giant day geckos
0.0.1 whites tree frog
5.0.0 dwarf hamsters
1.0.0 Bernese mountain dog
1.1.1 red ear sliders
0.0.1 emperor scorpion
0.0.1 chilean rose tarantula
1 planted tank with dwarf cichlids and platies