Nope. Seen them several times lately in the big jumper ring. I think they're less noticeable than colored breeches and all of the technical fabric polos, ratcatchers, and hunt coats! One of the rules/fashion folks can chime in here, but there's no reason you couldn't wear them in a classic. There are guidelines for formal attire for hunt coat color, ratcatcher color, and breeches in the rule book, but no requirement for boots.
__________________________________ Forever exiled in the NW.