The addition of white to most common camouflage colors like grays and greens has the effect of graying them. The system which I follow was published in the "Official Monogram Painting Guide to German Aircraft 1935 - 1945" by Kenneth Merrick and Thomas Hitchcock. According to research by Mr. Pat Donahue the proportions of white to be added for scale effect are: 15% white added to the total volume of the base color for 1/32nd scale models, 25% for 1/48th scale and 30% for 1/72nd scale.
It doesn't mention 1/16th scale so guess a factor of 5-10% added to the total volume of the base color would be about right.