I have always had hyper-temperature sensitive feet. Usually, when it's cold, they'll get so cold I'll have to soak them in warm water.

I just noticed that when I put them in hot water after they feel like little Popsicles, they get kind of blotchy, corpse-like purple spots all over. This lasts for a minute or two, until they've warmed up, at which point they return to a normal fleshy pink. It only happens when my toes go from cold to warm.

Does anyone have any idea what would cause this?

Sounds like you may have Reynaud's. To keep your feet warm, get those foot warmer pads the hunters use....be sure to get the ones that are self adhesive. I get them at WalMart or the sporting goods store. Love them!

Be careful putting cold extremeties like fingers and toes into hot water, you can do some damage to the blood vessels. Naturally these blood vessels are very small in the fingers and toes and it doesn't take much to damage them. Going from cold to hot very quickly like that is not good for you, I would recommend not doing that anymore.

I think it would be a better idea to try and prevent them from getting that cold. Wool socks, foot warmers that hunters use, etc, will help out.