the color will not effect strength. Unless they use too much color or wrong density plastic. Black is the cheapest as it uses re-ground mixed in. Clear or semi clear is virgin plastic. (At least in making buckets.)
Buckets don't use engineered polymers, but firearms mostly do. There are differences between frames and things such as handguards as well. With over 10,000 families, there are significant differences. I spent 20 minutes in deposition yesterday trying to get an attorney to comprehend such. Commodity polymers such as polypropylene and polyethylene (most buckets) are not affected by colorants, but that is not the same as engineered polymers. Most products made from engineered polymers with strength requirements specifically do not allow re-grind. Also, Natural color can also be bought with regrind and many manufacturers use regrind in house.