I don't really like this because it would only really work if done well, and I don't think it can be done well without lots of code.
There are too many questions that would need resolving that would essentially make it its whole own coding thing. For example:
You get stabbed with a spear, this creates some fresh blood, how much blood is there? Does it spread? Did I apply pressure to stop the bleeding? Did I bandage it? Does bandaging a fresh-blood wound stop it from bleeding?
What if I get bit, the wound bled but doesn't spread, in fact its pretty small, but there IS still fresh blood on my sleeve. A small amount of fresh blood. Does this show up to other people?
I skinned a bahamet, i'm covered in blood AND guts - this should have a variety of coded things like blood, smelly, etc. But is their blood the same color?
I smash someone's brains in and get splattered in blood. This would be a much different blood effect than if someone had stabbed ME, or if I had blood on my gloves from skinning, etc.
I don't see how it could be implemented, so I'd rather not see it just take current existing blood code and add a timer to it. Or other nuisances. Like "oh I cut in sparring a few days ago now I'm covered in flies" thats not how it would really work either.