Star Trek long had a policy of never showing Spock bleeding. And not for any kid safe, no violence, or heroic character reasons. They had early on defined Spock as "green blooded", but trying to portray green blood or other exotic blood colors on screen rarely works well. Certainly not with the budgets and technology they were playing with at the time. It's one of those weird uncanny valley things. If you smear fake red blood on someone your brain accepts it and fills in the rest, even when real fresh blood doesn't look like Hollywood blood. But attempt an exotic color and your brain hits the brakes and goes wtf? At least for anything that your brain registers as more or less human. Stuff like Ridley Scott's Alien your brain is already so deep in the wtf ride that it shuts down and goes with it. This is also why that bright purple CGI blood in ST VI looks so awful. (The other more modern reason for avoiding showing Spock bleeding? Green blood makes fx work harder as it messes with and complicates the green screen process. Easier and cheaper just to avoid the subject.)