Mosquito two tone

So i got my Mosquito last weekend and when i brought it home and cleaned it after firing some rounds through it i noticed a area on the inside of the slide on the ejector side that looks scuffed i guess you could say now there is no wear on the barrel or where the shell ejects out so i dont know if thats how it came from the manufacture or what just looking for some insight

here are two pics not the greatest but
http://i1162.photobucket.com/albums/...1178660222.jpg

http://i1162.photobucket.com/albums/...1178631959.jpg

Any help is appreciated

I also forgot to mention that i didnt find any metal filings

Yeah I got the same thing scuffed after I fired 300 rounds I think it's normal

Aite guess im not real happy about that but ok thank you sir btw is yours a two tone or what model do you have?

Two tone sig sauer mosquito