Yeah, as others have said, things will be better if he either takes another few steps or turns and looks at you. At that angle, red isn't terrible for a side brain shot, but it's a bit hard to know exactly. Yellow is aiming at nothing important. Green can work, but the shoulder bone is massive. Better to be broadside or slightly quartering away.
If you do try red, and it doesn't work, you'll need a quick follow up in the body if he turns and runs.