dekruif;
Unfortunately, except for the passenger engines, specfically the E's from the Claytor era, SRR diesels never had a "white stripe". The technical name is Duco Aluminum Gray. It actually is an emulsion, and not a paint per se. The differences in the way the stripe appears, either white, or gray is mostly a matter of lighting, and weathering. The brighter the sun, or the longer the paint is on the engine, the whiter the stripe appears.
For a match of the stripe, the best appears to be Floquils SP lettering gray, with anywhere from no white mixed in to a 10% mix of white and SP lettering gray, depending on age of the paint. If you notice, the stripes supplied by Micrscale, show this very aspect. Most are "gray" but some are almost white.