Shell color preference is going to strongly depend on your intended customer's preferences. Chances are for most of the country they will want brown, but in some places they will prefer white. Green/blue/really dark brown are exotics they may or may not take to.
By far my preferred layers are commercial red sex-links such as the ISA Brown from Townline in Michigan. My other favorite is the Pearl White Leghorn from McMurray. Both commercial working birds that will outlay pretty much anything else out there. I also keep a flock of Easter Eggers.
My egg sales wax and wane with the University season so when classes are out my demand ebbs. In the fall it picks up again. Right now I'm selling about ten to twelve dozen a week. In a few more weeks this will start to increase until I'm at about twenty five dozen a week. I have a self-imposed ceiling of thirty dozen in a seven day period as that is all I want to fool with.