Try filling with nothing in the basket. If it's still grey with no clothing and no detergent, it's the water or some nasty buildup in the tub. If the latter, try running a HOT wash on an empty machine with some bleach to clean out the scummy mess.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]