I suddenly have blue spots underneath the surface of my skin. it looks like blood and it is on my leg. what could this be?

Veins/blood: If they're long thin blue lines or streaks, you're seeing veins and that's normal. If you're seeing splotches or large, wide areas of blue discoloration, that's bleeding under the skin and called "purpura." unless you've had trauma to explain it, that's abnormal and should be checked out immediately. A blood count, including platelets, will help to clarify the issue.