Why Would My Son In Law's Arm Turn Blue? He

Why would my son in law's arm turn blue? He is 26 and was not feeling ill. His arm felt cold. He flew to Las Vegas for a business trip. The weirdest thing is that half my daughter's hand turned blue recently (and I don't think Reynaud's was the reason why). They were both in the Caribbean this past year. What do you think? Blood clot? Any connection between the two? Never mind, I didn't realize there was a cost involved