Well, I think since your space and time are at a premium your options are going to be slim. You say, You cant grow them out , and then reap the reward of the better sales price. But, you should keep in mind that you are not going to be feeding them either.
The longer you keep them the more they will cost you!
You have to keep your goals in mind. If you are breeding for mottled, you cant be spending so much time and $ on the "extra Colors" that are going to be coming. To get rid of them quick, easy and inexpensive is the way to go. To get some $ for them is better then none at all, right? Plus you wont have the
added expence of feeding/housing them for 6mths+. Also, whos to say they are all going to be great? You never know. But sure you will get some. I wouldnt worry about the "what if great ones". It takes away from your goal.
And when you do decide to get rid of them. Get creative. There are alot of avenues to do it. Killing is not the only way. I am not apposed to that meathod by the way, I just am giving other options. Take them to a local feed/pet store you might be able to sell them on a regular bases there. Also, BYC, CRAIGSLIST, FREECYCLE, OR A LOCAL BARGIN CIRCULAR ( PENNYSAVER). People will come out of the woodworks if you advertise. Posting signs up on community bullitin boards works too. Getting ahold of local 4-H or FFA clubs. Kids love to use small chickins like batums for showing.Also selling your extra eggs before you hatch them is another option for reducing future #'s.
Ebay and Eggbid, and BYC are good to do that.
Bottom line you have to decide what is more important to you? Is it the space and getting to work soley on your mottleds? Or worry about the other colors and price and not have enough space for the mottled project?Just food for thought! Good luck!