One suggestion. Another is to spray paint the buckets or pots and add the soil when the paint is dry. That is something I did several years ago. They were going to be used inside and outside so I spray painted them with a brown color paint so that they would blend in with the other potted plants on the patio.Spray glue & tinfoil, to black out those pots
Try to use a paint that is made for spraying on plastic. It might still peel off after a year or so which means another quick spray which should take only seconds to do so they should dry quicker.