Well...
IMO it is best to start simple. Why not a simple one colour scheme?
Most German walkers look very nice in plain old Panzer Grey.
US Walkers would do fine in Olive Drab and British or Soviet walkers will do in any army green.
I found the Flames of War sprays very helpful...
So - apply the basic colour, add some bolt gun metal where it belongs, paint the tracks in a mixture of rust brown and Bolt gun metal. The a very good brown/ black ink. After that some careful drybrushing, some transfers and maybe some Tamiya weathering powder...
Result:

