Well, that's a very good question - and the answer is I think so. (I don't see it much, there's usually food in the way
)
I think it may be related to the individual snake pigmentation - my large female yawns pink, my two other males are noticeably darker inside, but particularly dark in winter when they are cold and not eating much.
Here are pics of of the sides of the mouths when two of them are eating - the pink one is my large female (from another locality) and the darker one is this snake's brother. I'm going to search around for more pics.