When did The Edge start wearing the knit cap (toque) instead of a cowboy hat or other?

I can't answer this completely, and it seems to me, from looking at various photos of The Edge, that he has certainly been seen wearing other headgear, even since he became known for wearing the toque. However, the trademark toque can be dated back to at least 1994, as seen in this picture. Apparently Mr. Evans has been losing his hair for quite some time, so has used various hats to change up his look a bit.

http://www.macphisto.net/gallery-photo_BonoEdge-bonoedge0282.html

I think that looks more like a black beret. When he wears a toque, he covers his ears.