Perhaps a white shirt provided it has red accents of some sort on it. One like this would be a good example: If you are wearing a button-down shirt, I would advise a medium blue; light enough to be summery and to not clash with the white, but dark enough to be considered within the same ballpark as the navy on the belt. There are many, many levels of “casual.” T-shirts and jeans constitute an outfit for the lower end of the “casual” spectrum, perhaps one degree above sweats, two degrees above underwear. I am in a tiny minority of people who believe this, but I regret underdressing for an occasion much more frequently than I do overdressing.
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