Ok, I understand why they turn blue and how/why the shed like they do, but why does the belly turn pink before?

I have read this entire thread and the links, but I either missed it or forgot and I'm sorry if it's already here, but I just don't remember that it was.

My guess is that bloodflow increases to get the lymph out there between the two layers of dermis. We only see it on the belly because it has no pigment. Yes, no?