The skin on my legs from lower mid calf to foot has darkened considerably in spots. i have an ulcer/blister on the side of my foot where it meets ankle that doesn't seem to heal. does anyone know what this could be? thank you for any insights?

Called "stasis dermatitis", ie. discoloration secondary to veins in lower legs. The ulcer is also commonly a problem secondary to the stasis dermatitis

The spots on the lower legs that you are describing are consistent with what’s called hemosiderin deposits. This is the iron and red blood cells that gets leached out into the tissues and absorbed by the body except for the iron pigment. This in itself is not a concern but it does say that you are having circulation problems in the lower extremities and should get evaluated