i have just purchased my4th diesel truck and i have a question on the new 08's?

My truck has 5700 miles and i am notcing that the exhaust pipe is black on my truck and when i look at others theres is still shiny silver....does anyone know the cause of this? My understanding was the new diesels were suppose to be cleaning burning.

Daniel

 

Mine is black also. However, another truck at the company I work for is still shiny. Both trucks have 7000 plus miles.