If the tenants do not comply with the agreement, as specified in your written tenancy agreement, and paint in dark colours this may be considered damages. In this situation you could serve them with a notice of early termination based on damages (Form N5) in which they have 7 days to correct the problem.
If they have already moved out, as of September 1, 2021, landlords can file an application for damages with the LTB within one year from the date the tenant is no longer in possession of the rental unit. The tenant must have moved out of the rental unit on or after September 1, 2021. However, in order to file this application with the LTB, you will have to find out their new residential address to be able to serve them.