My Middle Finger Turned Extremely Dark (black And Blue) Covering

My middle finger turned extremely dark (black and blue) covering from the tip 2/3rds to palm and there was no injury at the time. My fingering was tingling and lost feeling while this happened. I had salmon and sweet potato fries for lunch - first time that I've had this - usually stick with the salad bar at my work cafeteria. I was heading to the hospital and then it started to clear up. Please advise.