UP called it quartz green, and it's still used on Maintenance of Way cars, as can be seen in the new ballast cars they recently bought.

At one time, the standard was to have all maintenance of way rolling stock painted this green, and all mechanical department equipment (wrecker derricks, plows, etc.) painted silver, which is why you could see both green and silver cabooses in those services. Prior to this, all company equipment was painted silver.

Needless to say, they never got the 2 chosen colors applied to everything. Some mechanical department cars (traction motor cars, engine transports, etc.) ended up red while a lot of M/W equipment, such as old boxcars and tool cars, stayed in whaever paint they had when in regular service.

Since all of the mergers, boxcar red has been creeping into the mechanical fleet, and the exMP derricks were painted green and black, or at least some were. Some exSP company cars are painted a lighter shade of green.