What Causes Prominent And Darkened Veins In Hands?

Allof a sudden while washing my hands this evening the veins turned dark and looked like they were moving.Within 5 minutes they are back to normal.I am 79 good physical within the last 2 weeks.Even the palms of my hands turned darker looking.I went out for DimSum today .Had a very bad headache within 2 hours and tonight my fingers under my rings turned very black.Took a reactine for the headache because I had been trying to cut myself off the Non drowsy reactine and thought I might be allergic to something I ate.I usually take 1 reactine every day.What could have caused this to happen?