We have used both. Although the dark ones don't show the algae as much, there seems to be more there. I live in a colder climate than you, so I don't have as much problem with the water getting all that warm. So I use the dark ones now in the pastures where I don't have automatic waterers. I just don't like they way the gunk is more obvious in the white ones. Oh, and it's much harder to find them here. Mostly the dark gray Rubbermaid ones and aluminium ones at the stores here.