Pretty simple, actually, except when the gene pool is mixed.
White x brown = lighter brown.
White x blue = blue.
Blue x brown = green.
Blue x green = more aqua.
except when it doesn't
Do a thread search for sex-linked information to find an awesome set of charts for your future chicken...
When a hen or pullet starts a laying cycle, the eggs are as dark as they will ever be. As she progresses through her cycle, they typically lighten up a bit, till she starts the next cycle.
You have some EE or Ameraucana genes in your mix. I'm betting EE. How sweet! I love my EE girls. Keep an EE roo to keep the egg colors interesting. He makes a nice black sex link green egg layer chick when crossed with Dominique or Barred rock.