What Causes Discoloration Of Knuckle After An Injury On Hand?

Hi - I'm a 56 yr. old female, 5'4", 114 lbs, on two different anti-depressents. (medium doses; not high.)

My pinky on my right hand is discolored: darker color than unsual, reddish tinge, and even darker at the knuckle. This discoloration runs down the top of my hand too, 3/4 of the way to my wrist. I vaguely remember hitting that part of my hand into something yesterday, but it was extremely minor, and didn't hurt much at all. Then today I wake up, and it's this shocking color; suddenly! Is this only trapped blood from a bruise? I can make a fist, but very gently. Is the reason the knuckle is the most discolored because the blood has pooled there??