The enhanced line was introduced in 1992 as the premium counterpart to Colt's budget 1991A1 line and really only existed in the 90s until it was replaced with the XS and XSE line.
It has a flat raised rib on the top of the slide, more aggressive slanted cocking serrations, 3-dot sights, undercut trigger guard, skeletonized rowel hammer, duck bill extended grip safety tang, beveled magazine well, and usually came standard with Pachmayr wrap-around grips.
While the enhancements are pretty tame by today's standards (in fact, most new guns come with them off the shelf) they weren't AS common in 1992 and definitely not on stock guns.