Both my hands, all fingers, turn actually blue at the same time.
(Milwaukee, WI, USA)
For the past 5 months, I've had intermittent instances where both of my hands and every finger will turn blue. My hands will be normal temp. The blue stops at the wrist. The veins are not distended. My hands are not swollen. I have no tingling, pain, or numbness. I have no known medical conditions. I have no other areas of cyanosis. My nails are normal.
My hands will stay blue until I move them around. Usually the bluing comes on after sitting at a table with my elbows on the table, with my hands hanging straight down like when walking; and especially when my wrists are bent backward with palm up.
What is this?
It's likely to be Reynaud's syndrome. There's no known cause or cure. However I find rubbing the hands and arms certainly does help, and sometimes chiropractic manipulation of the cervical spine, though I know of no research confirm this, so treat it as an anecdote.
Ask a friend to massage your whole arm and hands regularly for a few minutes. You can do some of it yourself.
It's a disturbance of the sympathetic nerve supply to the blood vessels in the lower arm.