Maybe these links will help
Egg colour genetics
https://scratchcradle.wordpress.com/2012/07/01/gms1-genetics-of-egg-color/
https://scratchcradle.wordpress.com/2012/07/08/gms2-breeding-for-blue-eggs/
https://scratchcradle.wordpress.com/2012/07/15/gms3-breeding-for-other-egg-colors/