I have a 2005 5.4l 3v and today I was cleaning the undercarriage. While I was doing that I noticed my exhaust an odd color. This isn't rust is it?

Here are the pics

 

Looks like dirt and ware and tear. Mines like that for my header to the y pipe. I replaced with a catback mbrp. I drive through everything so I'm sure that's what it is.