What color would be better? Green seems like a poor choice when telling someone not to park there.. Yellow is already taken (loading zone). Blue is already take

What color would be better? Green seems like a poor choice when telling someone not to park there.. Yellow is already taken (loading zone). Blue is already taken (handicap). Orange is close to yellow, and is that even better in the dark? Signs for every single red zone is overkill (there are red zones on the edge of garages for example).