I think you are correct that the landlord should not expect the useful life of paint to exceed 6.5 years. Moreover, since you didn't paint the walls in super dark tones which would require an extra coat of paint, there is no justification for the landlord to pass on the cost of painting to you.
Unfortunately, there is nothing specific under California law regarding this specific issue.
However, you might find the discussion under Repainting Walls under the section on SUGGESTED APPROACHES TO SECURITY DEPOSIT DEDUCTIONS at the following guide to be helpful:
The information presented here is general in nature and is not intended, nor should be construed, as legal advice. This posting does not create any attorney-client relationship with the author (who is only admitted to practice law in the State of California). For specific advice about your particular situation, consult your own attorney.
Look at the lease, and then pull any paper work where he grants permission (or variance from any requirements in the lease as to repainting and color). After seeing what was agreed to in those two instances, consider the question again and speak with an attorney. The attorney should be willing to back up his analysis with representation should it come to that, and include his lawsuit details and fee in the attorney client agreement.
This way, you will have some idea what this will cost for a full trial, along with the precedent, and then you can make a decision to fight this or not.
Curt Harrington Patent & Tax Law Attorney Certified Tax Specialist by the California Board of Legal Specialization PATENTAX.COM This communication is general information and not legal advice, and does not create an attorney-client relationship. This communication should not be relied upon as any type of legal advice. Please note that no attorney-client relationship exists between the sender and the recipient of this message in the absence of either (1) a signed fee contract and (2) remission of an agreed-upon retainer. Absent such an agreement and retainer, I am not engaged by you as an attorney, nor is any other member of my law firm.