There is a site called the Circle of the Dragon that goes into great depth into the meanings of color and how we assign them. Specifically it goes into each color of the dragons represented through myth and fiction. Below is an except from http://www.blackdrago.com/colors.htm
For example, the first of the Dragons' Geas novels involves a Blue Dragon. The writings about Blue Dragons specifically were influenced by this website.
"Blue is a common color for sea serpents. Light blue dragons represent the vastness of the sky and flight, while dark blue dragons represent still, deep waters. Blue dragons are highly protective creatures and magical.
Blue Chinese dragons are of the purest azure colors. They are a symbol of the East and are pacifying."
Kylie 'drago' McCormick
This is a great site to visit and I encourage you to explore it as a writer and lover of dragons.