Did you ask if these chemicals are harmful to the plants? Do the plants systemically uptake these chemicals and are the chemicals then contained in the plant and released upon consumption? Seems like these would be prudent questions to ask.
Dutch Master recommends using high density plastic, with mid density being acceptable. Isn't necessary for it to be 'food grade'. Low density will leach chemicals which they do not claim to be harmful, but will mess with the nute balance.
As for the color letting in light, you can always cover them with paper, foil, ect. You could also inoculate with beneficial microbes which do a great job of discouraging algae.