Sartorial Faux Pas (?) -- Mismatched Belt/Shoes (I Did It Anyhow)

Years ago a rather stylish female friend chided me in tough love fashion on some combination of shoes and belt, telling me they always had to color coordinate.

Well, in anticipation of Spring, I dug out my cordovan wingtips for work today. But I determined that (hey, maybe a good thing, I’ve dropped a few pounds) my brown/cordovan belt really doesn’t fit. So I went with my usual black dress pants belt.

(a) Was/is the rule she cited really a rule?
(b) If so, is it still?
© Just what degree of gaucherie, if any, am I guilty of on a 1-10 scale?