I think the black plastic may well overheat your plants. I have several dark containers and have only recently learned of this problem. I've moved many of my black pots behind other lighter-colored tubs to try to shade them . Also when I recently had a choice between planting in a black container or a light gray one, I chose the light gray tub. It's all I can think of doing for now. Hope this helps.

What about painting them with a spray paint for plastic?

I've painted a few of my black nursery pots a light yellow. I've still tried to only plant shade plants in them, but I wondered how much it would help reduce heat intake.

Yellow is very attractive to some pests, particularly whitefly. Cover with tanglefoot and you'll have the ultimate fly catch... ;)

I shade my black planters with pieces of plywood et al. I also throw a couple inches of bark mulch on them also I did, however, paint some clear water bottles WHITE that I converted to planters.

Kevin