From what I've read recently, the dress tartan was simply a variant of the "clan" tartan (as opposed to the chief's tartan) and was worn for dressy and "state occasions." If it was only, or primarily, worn for special occasions, I don't think the lighter colors would present a major soiling problem. I was looking at references from the late 1800's and early 1900's, and I did not see any reference to the dress tartan being a ladies' tartan. I did however, see several references to the head of a clan wearing the dress tartan for a special occasion, and elsewhere of the chief wearing his reserved tartan and the others in the clan wearing the dress tartan. It would be interesting if try to determine where the myth about the dress tartan being for ladies originated. From what I've read, at least 100 years ago, that attitude was not common.