Welcome to the Forum!
I would dip my finger in it and smell it... it might have unburned gas, if it smells really gassy, it might be time for a tune-up, check error codes, stuck float on the carb, or ???
Other than that, did you recently take it under water or splashin'? There could still be water coming out of the muffler and it would look rusty like that.
If it smells real gassy, get it looked at by a pro right away. We don't need any Jeep fires, especially after Chadwick dunked his Jeep in a pond the size of Lake Michigan to impress his girlfriend... We need a little while without loosing any jeeps
Oh, and great job getting a picture right out of the gate. It really helps us to see exactly whats up. I'd tell you more if we could make it a scratch and sniff