Here are the books I read for this challenge:
Green - Before Green Gables by Budge Wilson
Yellow - Travels in the Greater Yellowstone by Jack Turner
Red - Big Cherry Holler by Adriana Trigiani
Brown - Bitter Chocolate by Carol Off
Black - Riding the Iron Rooster by Paul Theroux
White - The Little White Horse by Elizabeth Goudge
Any other color - The Orchid House by Lucinda Riley
Any implied color - The Color of Rain by Michael & Gina Spehn