T-12 "shot" in color Green Jacket

I was perusing a book on the watercolors of the great American Artist Edward Hopper the other day, when I saw a painting of D&RGW T-12 #177 done on the spot and out of doors in the yard at Santa Fe. The engine very plainly has a medium green jacket.
Hopper was famous for painting deserted cityscapes, industrial landscapes and The grittier side of small towns. When He Visited Santa Fe in 1925, he looked around town and told his wife there was nothing to paint. It's too beautiful, he said. His wife took a nap, awoke alone and found him in the railroad yard painting an engine.
On another note, anyone know why the RG and the WP painted the main axle ends of some engines red? I know the SP pained stars on some axles to denote a spring loaded grease cellar or some such. Anyone know?