I don't think it's an addiction to drugs, as it's been mentioned before. You would aim for a vein, not miss it, and clearly when he was in the hospital the nurse said he missed veins. I think it's definitely about cutting, as cutting is also an addiction. Dopamine and other lovely neurotransmitters being released and all that. Also, getting "closer" in the hospital ending would be cutting deeper. But it could be interpreted very differently, and I like that.
The colour feels like a punishment. It's not good colour. It's obscurity. Obeying makes me feel... strange, but I much prefer it to disobeying. It didn't spawn as much existential questions as it did turn me on, though.