You are positively "evil"; I like you so much.
Wouldn't blood get lost in the grass? Could work on bare ground and on rocks. And maybe people who turn off the grass would gain an advantage if blood would show in grassy areas, which the grass would ordinarily hide...
Evil is half the fun in the game, its not enough to just kill someone, you want to outsmart them...make them feel like a caveman for contesting your intelligence. As for the blood hiding in grass, yes if it was just a pool on the ground it would...maybe have it die that grass red?
I don't wonder if there would be a problem with a mechanic where if someone did bandage themselves they would still leave a blood trail, at least for a while.