[I had a fresh bottle of Floquil's diesel light blue and a bottle of white to work with. While they call it light blue, I found by using it straight it worked nicely for trim, and by mixing in a good deal of white I finally evolved a small bottle of really light blue that suited me fine. E. L. Moore in his Grizzly Flats build article on how he chose his colours.]
I was checking colours for the real Grizzly Flats depot online and it appears to have been - approximately - yellow with brown trim. Not blue. On my N-scale version I used Polly Scale GWT Blue for the trim and mixed it with white to get the light blue panel colour.
I drew the diagonals on with this Micron 0.005 pen. They're a little dark for my liking, but I think they'll be ok once the roof is on and some other components are installed.
[You can panel the outside wall if you want to. I left mine plain. E. L. Moore states that he didn't do any detailing on the rear wall - and it's never on view in any of the article's photos.]
I went ahead and trimmed and panelled the back wall because when the depot is placed on the EVRR all sides will be visible. It's all guess work, but it fits in with the general patterning on the other walls.
There's lots of touch-up painting to be done, and I'm looking forward to building the bay window and, especially, the roof. The building itself seems rather plain. I think it's the roof that makes this thing pop.