Obviously, a white water bottle will stay cooler than a black one on any day where it's exposed to the sun. If you want the water to stay cold, insulate it. Color doesn't matter as much then.
Camelbak Podium Ice will keep water cold for 4+ hours in +100º heat, which is more than enough-- because that bottle will be empty in less than 2 hours anyway (often significantly less.)
On cooler, sub-90º days, I've still had ice in the bottom of the bottle after 6+ hours.
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