Apple Watch band colors

I'm not sure I understand your question? You can only wear one band at a time on an Apple Watch. But if the watch has two pieces, you can use one piece in one side and another piece in the other side, which if they are the same style band (such as Apple Sport Band, which is a two piece band), you could certainly wear one color on one side and another color on the other side. But they'd have to be of the very same type band for the clasp/closure to lock the band on your wrist.

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