MILW color schemes could fill a book...

Here is a quick rundown of MILW diesel paint schemes.

Earliest diesels (pre-WWII) -- black, white lettering on hood.  At least one SW1 was painted silver, didn't last long.

Freight schemes - Early F-units were grey, with orange lightning stripe.  In 1950 or so, they went to orange and black, with the maroon band in the middle.  Passenger units also received this scheme, which matched the cars.  Early switchers and road switchers received the "coach" colors, grey top, maroon stripe, and orange, with black frame and trucks.  A handful of switchers had black on top, maroon stripe, and orange.  Starting with the SD7s, the familiar orange and black started, with the color break line roughly at the radiator grille level.  Later the break was moved down to about the bottom of the cab window.  Cab units lost the maroon band in the middle 1960s. Billboard lettering on the hood sides and nose started around 1973, on new and repainted engines.  The Hiawatha scheme (with the running Indian sticker on the nose, and a small lightning stripe on the hood side) started in 1982.

Passenger schemes - The DL109s and E6s had a slightly different grey and orange lightning stripe scheme than the F-units, which didn't match the cars...  The E7s also had this scheme.  The FM Erie-Builts had 3 or 4 different schemes.  With the FP7 deliveries in 1950 or so, the orange - black - maroon band started, and most passenger cab units got it.  In 1955, MILW took over the Chicago-Omaha leg of the UP Streamliner fleet, and it was found that the UP yellow and grey didn't look horrible when dirty, so most passenger equipment was repainted, excepting Chicago commuter service cars.  The yellow and grey lasted up to Amtrak's formation in 1971, with commuter service engines retaining the colors until they were replaced with F40Cs, which have a fairly unique scheme, and stainless steel fluted panels added to the sides to match the cars.  F-units that went back into freight service usually kept the UP colors until retirement. 

There are plenty of one-off schemes that made it out of the shop.  Pictures are a good guide.  For example, some freight F-units got UP-style lettering along the sides.  2 FM switchers were painted yellow and grey for Milwaukee depot switching.  3 passenger GP9s were painted yellow and grey.  The MILW painted things differently that the UP did, of course.