Grayson says black clothes are "an abstention from the conversation," which I presume means they don't contribute anything either aesthetically or in terms of expressing anything about the wearer. I'd say what they express is a group identity, at least on cyclists of the rapha-wearing sort (other manufacturers are available and applicable). Away from cycling they can express other things, as when worn by "skinny paranoid chain-smoking New Yorkers,"* Johnny Cash, priests or anarchists. (I don't smoke, have never been to New York, can't sing, am not a priest and am not comfortable with anarchism, so I only have black socks.)
I note he specifies this only applies to black clothes on men but I don't know if that's just because he's writing about men or black clothes on women do take part in the conversation.
*Quote from someone but I can't remember who.