I'm imagining he's going to some sort of event or party where there are teams for a game, maybe red and blue, and everyone is supposed to come dressed in their team colors, so even though there's white, the red is sufficient to signal his team/shirt color.
Or maybe a party with a color scheme, and he's reassuring the other person that he is indeed wearing red as promised, and as is often true of color schemes, white gets a free pass.
I'm imagining he's going to some sort of event or party where there are teams for a game, maybe red and blue, and everyone is supposed to come dressed in their team colors, so even though there's white, the red is sufficient to signal his team/shirt color.
Or maybe a party with a color scheme, and he's reassuring the other person that he is indeed wearing red as promised, and as is often true of color schemes, white gets a free pass.