I don't know, but your hypothesis is as good as any. Have you noticed if the color corresponds with the temperature? I'd think if it was warm or if a cat had been active, that's when there'd be more blood flow.

 

When Lucas is excited/playful, his nose goes from ice pink to a bright rich pink. I always assumed it had to do with blood flow. When he gets like that we call him Mr. Pink Nose and chase him around the house. He seems to like it .

 

I'm no expert, but I think it could be like our faces get flushed when we exercise or are hot. I wonder if more of their face, hidden under fur, also gets flushed?

 

You know, I do notice it is pink when she is excited and running around or playing. It is white if she has been laying down or sleeping. Though if I pet her and get her to purr, the color will come up.
I just thought it was odd. I'd never had a pink/white nosed cat before.