Painting a wall that you don’t own is a form of vandalism under most property laws, unless you have written permission from the owner or the landlord; that’s the plain reading of the statute. If the owner is a landlord, the lease usually includes a clause that you must not alter the premises without consent, and a breach can lead to eviction. Even if you’re a tenant, the common law tort of trespass to property applies if you deliberately damage the property—painting is a form of damage. So unless you have explicit consent, you’re risking a civil claim for damages and possibly criminal charges for vandalism. In short, it’s legally risky and likely illegal without permission.

Sure, you’ll have a colorful “masterpiece,” but the law’s still on your side of the wall. If someone takes you to court, the judge will ask whether you had permission—if not, that’s vandalism, which is illegal. So paint with gusto, but remember the risk: you could end up with a fine or a court order to fix the wall, and that’s not a bright splash of paint, that’s a red‑label in your legal ledger.