Right hand twill and left hand twill have a couple of different characteristics, one is how they fade. The fade on LH twill generally looks a bit blurry compared to RH twill. See below for a comparison between Studio D'Artisan SD-101/102(RH) and SD-003(LH).
(In Studio D'Artisan's model numbers, the first digit specifies which denim is used, and the third digit refers to the cut. 103 and 003 are the same cut but different denim.)