The NZ Metal Roof and Wall Cladding Code of Practice is a comprehensive design & installation guide, and a recognised related document for Acceptable Solution E2/AS1 of the NZ Building Code.
Because painted roof lights appear no different in place than metal sheets, this practice can be dangerous for any workers carrying out maintenance work on the roof. Painting can also cause heat distortion which can lead to premature failure.
As a warning, primary and secondary fasteners can be brightly coloured, providing a contrast with the remainder of the roof cladding surrounding the roof light areas. The area can also be marked around with a distinctly painted stripe.
Lichen will accumulate on plastic roof lighting wherever there is a source of nutrients, but it should be removed with care. See 15.7.1 Lichen And Mould.