I have bunch of scars from my flat pedals. Color of the scar depends on the depth of the gash you have on your leg, mine ranges from deep purple(really deep cuts) to barely visible white discoloration.

I got to tell you this though...When I used to ride fire roads only I used clipless pedals but when I started do very technical single track I went back to flats because of the idea of getting stuck on my bike while I was coming on some down gnarly rock garden scared the crap out of me and ironically most of my injuries or scars happened because of the flats because no matter how hard I pressed on those pedals somehow they would slip and put a gash on my shins or back of my legs. So about a month I decided to give clipless pedals another shot, first couple rides were bit scary but once I got use to them I had so much more control over the bike it's crazy. I actually went and bought a pair of wellgos with one side flat and one side clipless and I'm telling you I won't be going back to flats ever again. Ok I'll use the flat side of my pedals when I take my bike to the beach.
And I almost forgot since I put the clipless pedals I haven't had a scratch, in fact I had two pretty good spills one yesterday and one today both times my feet came off just fine.