Seems like it could be a tradition to do so since Vulcan ships were seen as Red in First Contact and then again on Enterprise, (although those were pre-Federation design). You could assume that Vulcan's enjoy Redish colored ships.
you forget, the "red" was apparently retconned out to a dull turd brown in later seaons, AND there would be no connection, as no-one had thought to bother with vulcan design, yet, in the 80's.
THIS is the shuttle I thought you were gonna work on, originally.