It gets pretty close to 100+ degrees here in FL in the summer months. My water containers get 8-10 hours of sunlight during the summer. As long as the plants are getting cooled by water, they should be okay. But I suppose it depends on the plant species. There are some marginals that naturally grow in shade. My advice would be to google the plant name to see the growing requirements and the light requirements. Containers can be moved if necessary. I do use light colored containers whenever possible, but my two large 35 gallon round preformed container ponds are black. I have NOT lost any plants or fish in them during the the hottest part of the summer. The mosquito fish are pretty tough. Goldfish or Koi might not be.
You could also plant some plants in the ground around the containers to shade the base of the container to bring the temps down. Waterlilies and Lotus do not seem to mind very warm water. In fact, they seem to thrive in warmer water vs. cool water.
