That's a tough one. 1991 SM500 was black with white web but had red decals, had SunTour X-1 build, and the Cannondale decal was on the down tube. 1990 bikes had the Cannondale decal on the top tube but the catalog doesn't show any colors with the web color over the base color. In both years the XCM bike was the SM400 and all the models mentioned had a steel unicrown fork. The closest bike in the catalogs is the 1991 SM400, as it was offered in black and Mystic Blue with white web, and was equipped with XCM. Perhaps your bike is early production or prototype.