Answer: By way of refresher, ORS 90.630 pertains to curable maintenance/appearance violations relating to residents' spaces. However, if the violation relates to the physical condition of the home's exterior, ORS 90.632 applies, to address repair and/or remediation that can take more time to cure, either due to the weather, the amount or complexity of the work, or availability of qualified workers.
SB 277A, became law on June 14, 2017 ("Effective Date"), applies: (a) To rental agreements for fixed term tenancies - i.e. leases - entered into or renewed on or after the Effective Date; and, (b) To rental agreements for periodic tenancies - i.e. month-to-month tenancies - in effect on or after the Effective Date.
Both ORS 90.632 and the MHCO form (No. 55) provides that if the tenant performs the necessary repairs before the end of the compliance date, or extended compliance date, they have the right to give the landlord/manager a written notice that the issues have been corrected. There is no fixed time for management's response as to whether the repairs have been satisfactorily and timely performed; it is sufficient if it is within a reasonable time following the tenant's written notice. However, if a tenant gives this notice to management at least 14 days prior to the end of the completion deadline, or extended deadline, their failure to promptly respond is a defense to a landlord's termination of tenancy.
I am assuming the tenant gave you no such notice, otherwise, you would have responded that the color was too bright.
MHCO Form 55 contains a prompt at several places to attach additional pages, documents or photos, if doing so would be helpful in identifying the disrepair or deterioration, and the necessary repair. As I said in an article last year on this form, '_you cannot expect the tenant to be a mind reader - just because you know the nature of the problem and the appropriate repair, does not mean the tenant is on the same page. If there is any ambiguity in the notice, a court would likely rule in favor of the tenant. Why? Because the landlord/manager filled out the Notice and had the ability at that time to draft it with sufficient clarity."
Is there a technical argument that since the requirement was not in the Form 55 Notice, that it is not effective? In other words, he complied with the Notice, but not the letter. As you said: "He did paint like we asked him, but it was not a color approved by management." I personally think such an argue is specious - assuming that the letter accompanied, or quickly followed the Notice.
But to the question whether you can proceed under the Notice, I don't think I would recommend that, because the Notice was complied with. Assuming you have some rule about pre-approval on painting in your rules, I would issue a 30-day notice.
If you do not have such a rule, you will likely have to tread lightly, as you may not be in a good position to declare a violation upon which to issue a termination notice. In other words, you should try to reach a compromise, which may result in some form of cost sharing. I'm sorry to reach this conclusion, but without the requirement of management approval somewhere (i.e. in the rules or the Form 55 Notice) you may find that it the tenant secures legal counsel, you options are limited.
The cautionary tale here is to make sure that when issuing Form 55 Notice, you not only need to identify what the problem is, but all completely explain what is necessary to cure. Had the pre-approval requirement been set out in the Form, you would have at least had a reasonable argument of non-compliance. I say "reasonable" because there still remains an argument by the tenant that you are imposing a requirement (i.e. management pre-approval), that is not contained in the rules or rental agreement.
 There is an argument that the Letter was part of the Form 55 Notice, and therefore the tenant is in violation. However, unless one of them referred to this cross-reference, it is not a pitch I would try to make in court.