Apologies to those who've heard all this from me before, but it sounds like it might bear repeating:
I've clayed extensively since (mild) detailing clays came out around 1990, and I never had a problem with marring until I tried the *current version* of Sonus gray. It's simply more aggressive than I'm used to using. I've played around with it and on some paints it simply does mar, even with plenty of proper lube (I use Glyde) and with appropriate/minimal pressure. NO, it's not like an overspray clay, but it's not all that mild either.
Note that, having used Sonus "gray color" clays for quite a while, at first I didn't believe it would cause marring if used correctly.
RAG sold me his Sonus gray because it marred for him and he knew I was a big fan of Sonus clays. I was

when I used it on my M3 and *really* marred it up. I was so amazed that I contacted DavidB to find out if it might've been from a defective batch! No, it's not defective and no, I didn't misuse it- it's just a more aggressive formulation than the previous Sonus Block/gray clay.
The previous two versions of Sonus gray did *not* mar unless you misused them. I don't know just when the formula switched. The green Sonus Ultra-fine clay won't mar unless you *seriously* misuse it.
The marring from the current Sonus gray does polish out rather easily, but I don't like this marring and thus I reserve it for use on stuff like the back sides of wheels (worked great for that just yesterday), or really nasty contamination. In these cases I know I'll have to polish anyway.
There are other clays that are quite effective and *do not* mar if used correctly. Of these, my favorite is the expensive (and out of production, so buy it while you can) SmartWax clay. It's the same as the *first* version of the Sonus gray (other than the color) and it's wonderful stuff, as well it should be for twenty-some bucks a bar. Others can suggest less expensive alternatives.
For light claying the Sonus green is great and it won't strip a healthy coat of LSP.