UPS brown is a color called pullman brown. UPS copied it from a rail line that painted its cars this color. You can try some of the railroad lines of paint, or use Testors gloss brown #1240 which is close.
I took a break from airplanes after 25 years of building them. That was a couple of years ago and I have no plans of going back. I enjoy car kits much much more...welcome to the other side
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Darren