Here's a really great page with tons of information.
http://utahrails.net/drgw/rg-diesel-paint-schemes.php"Color Notes
1. Two shades of yellow are referenced below. The first color, usually known as Ochre yellow, was first used in 1941 on the first 15 yard switchers, and in 1942 on other units. It was a lacquer paint with the trade name of Dulux Gold, similar in color tones to today's Dijon-brand mustard. This color was often used to simulate gold leaf. This color had the trade name of "Dulux Gold," and should not be confused with the later paint that used the trade name "Dulux Imitation Gold," which D&RGW began using in 1946.
2. The second yellow color, first used in 1946, was the result of the chnage from lacquer paint to enamel paint. The later yellow color had the trade name of Duco Imitation Gold (DuPont color 246-54015). It was a lighter and fairly bright yellow, compared to the earlier ochre yellow, which had darker tones. In later years, the newer yellow faded to a creamy yellow color.
3. D&RGW's famous Aspen Gold, also known as Grande Gold, had the formal name of Duco Orange (Du Pont color number 254-6479; EMD color number 8173994). Aspen Gold was adopted for freight equipment and cabooses in early 1956. It was first used on the Prospector passenger equipment as early as 1950, and on locomotives as part of the four black stripe scheme in 1951. The color first came into use in 1949 as the Aspen Leaf scheme on the noses of the Alco PA passenger cab units, and on the narrow gauge C-16 2-8-0 268.
4. Beginning in the mid 1920s, DuPont produced two types of paint; Duco lacquer and Dulux enamel. Duco was a lacquer formula dating from 1923. It held its gloss better over time and stood up to regular washing better, and being a lacquer, took less time to dry. Duco was also more expensive. Dulux was an enamel formula introduced in 1926. It took longer to dry (usually overnight), but was less expensive. Dulux enamel was more resilient and resistant to chipping, and was a better choice for locomotive and car running gear. Many railroads, including D&RGW, specified Duco lacquer for use on the carbodies of their diesel locomotives, but continued to specify Dulux enamel for use on locomotive running gear. (Read more about DuPont Dulux and Duco paint)
5. Aluminum paint color, sometimes known as bright aluminum, was used to simulate polished stainless steel. Depending on the needed durability, both Dulux Aluminum and Duco Aluminum were used."