The following definition comes from the Cub Scout Leader Book 1997. "Blue and gold are the Cub Scout colors. They have special meaning, which the boys and leaders should understand, and will help them see beyond the fun of Cub Scouting to its ultimate goals."
Origin of the Blue and Gold Colors for Cubs
Denver Area Council
Here's the explanation, taken from page 271 of the 1961 printing of the Cubmaster's Packbook (BSA #3200):
"Blue stands for truth and spirituality, steadfast loyalty, the sky above.
"Gold stands for warm sunlight, good cheer, and happiness".
According to the 1939 Cubmaster's Packbook:
"The Cub colors…signify the loyalty as symbolized by the true blue of the eternal skies--while its gold represents the brightness and worth and light of the Cub's smile and happy ways."
Cub Scouting American Style
Our Cub Scouting is different from the younger-boy programs of any other country because it is home and neighborhood centered and is built around in-between-meeting-time activities. The program suggests a wide variety of interesting things for a Cub Scout and his den to do, with the encouragement of family and leaders. It suggests activities that boys enjoy doing on their own, when not under adult supervision. These activities are particularly suited to boys of Cub Scout age and are kept quite different from those they will encounter in Boy Scouting.
This tip is from just a small section of the Cub Scout Leader Book, "History of Cub Scouting", pages 1-7 through 1-10.