Now I don't want to get into the logics of comic books, or how silly it is for characters to wear colors that don't seem likely for their theme, the few there may be (Spider-Man), but it always bothered me that a character whose name is Wolverine, whose a naturalist, and who got his costume long before he joined the X-Men AND before they started wearing the blues and yellows, would wear a blue and yellow costume instead of some colors that a wolverine/wolf/wild beast would sport.
Brown. It just looks better and makes the most sense.