Sudden symptoms: blood rushing to hands, blue hands, white knuckles, blue fingertips. -- help?!

[ClariceG]

Beginning about seven or eight months ago when my brother and I would go to Del Taco, he would purchase a Cherry Coke and soon after drinking it his hands would start to "cramp a little", and the fingertips would turn blue. It got progressively worse, and we decided that he should switch his drink flavor over. The sudden rush of blood to the hands quit for a little while, but came back.
This evening he was drinking regular coke and had eaten Chicken Soft Tacos, and his hands were "Cramping", up into the forearm, and his hands including the fingers were a blue color. He said he felt very lightheaded and like his chest was "hollow" (he said it wasn't a good way to put it, but it was the only way he could think of to describe how he felt; I asked if he meant "light", but he said no, like a hollow tree.). In the past his hands have turned blue, with the knuckles from the base of the fingers to the edge of the fingernails (at the cuticle) pale white, and then his fingertips blue. Now the whole hand is blue.

Half an hour after eating, his hands are normal, he isn't hollow, and he's not dizzy.

I believe this to be a food allergy, but I don't understand why it doesn't happen anywhere else.. Thoughts? Has anyone experienced this?