Q. My dog had diarrhea and blood would come out but hasn't had it for a couple of days
A. Fresh red blood indicates bleeding low down in the intestinal tract. If there are no other symptoms and it is just a small amount once or twice then I wouldn't worry too much especially if your dog is better now. It may have been something that it had eaten that didn't agree with it. If it is excessive amount of blood or any other symptoms then you should see your vet.
dark red/black coloured indicates bleeding high up in the gastrointestinal tract which is more serious and should be checked out straight away.