What color is it? A photo would be helpful.
The picture I was looking at was of a fairly new car, so I think it might have been the angle. (Car was new in 75 and the pic was from 77.)
The bottom of the car may have accumulated a great deal of dirt along the bottom over time, since dirt was what the Milwaukee used for ballast.
FRRYkid,
I just consulted the "Milwaukee Road Color Guide to Freight and Passenger Equipment, Vol.2 by Doug Nighswonger from Morning Sun and found three pictures of 2600 cu. ft. Airslides but couldn't tell for sure but, of the seven 4180s in the book, it was easy to see that the undersides were the same grey as the rest of the car. I would say dirt is what makes it hard to be definite on the 2600s but horse sense says if the 4180s were all grey the 2600s were also.
I recently purchased a Walthers Milwaukee Airslide hopper. In researching the car to make sure it was correct, I have come up with a question. What color is the bottom of the car? It might be the angle of the pics but it appears the bottom is black. However the model is gray. As usual any assistance that can be provided would be most welcomed.