“Can I paint outside of a clear bin to have my worm farm in? thanks” ~ Dot Wildman
The reason why all worm bins are non-porous for light is because worms are very sensitive to light and will not work to their full capacity when light is shone through.
Painting a clear bin will work because it can block light from entering into the bin. You will need to make sure the paint that you use can serve that purpose.
Some paint can be very thin and may need a few coatings before it can block light from entering. Acrylic paint is a good option. Using dark colors will be most effective blocking light, but if you live in a hot climate area (especially with summer here), dark colors may also trap too much heat which will not be too good, and a lighter color will be more preferable.
Make sure that when you paint the bin, that you paint it on the outer surface (non contactable with worms) and not the inside. Paint contains solvents and thinners which may be harmful to worms. Happy Painting!