My moshi leaves marks. but I had it for almost 2+ years. warm water+soap cleans the cover nicely.
I also cover the keyboard with a thin micro fiber cloth.
I love my Moshi Clearguard. I made a video review I can link you to if you're interested. It does get pretty dirty over time but ten minutes to clean it and it looks great again. Have not noticed any heating problems except very slight increases when gaming. It keeps my keyboard free of debris and will keep my keys in pristine condition by protecting them from wear over time. Love it and having tried two others, this is by far the best.