I almost always wear black. Sometimes it's "spiced up" with my Gordon tartan scarf; sometimes with jewelry. Winter it's long sleeves. Summer it's short or sleeveless. But it's almost always black. [Sometimes, I'll go for a hint of color and do dark green]. The only time I don't do black is for RennFaires or SCA events -- which are usually summer and hot.
Black comes from long years of classical concerts and from the general tradition of the musicians being "invisible" in performance in traditional times. Rumpled, it still looks fine. Hot, it doesn't show sweat. It covers a mass of physical "anomalies." And I feel comfortable in it.
Most of the local scene wears flannel shirts or t-shirts and jeans in varying degrees of rumpledness.