I had this idea a while ago to do a photography project about items that need to be a specific color to work. More specifically, things that wouldn't work if they were a different color, such as camouflage, litmus paper, traffic lights, etc.
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Oranges. If they're blue, then they're called blues. They must be orange, otherwise they will not be oranges.
Paint. While it can function in any colour, it's correct and proper function isn't being fulfilled if it is wrong.