I would like to keep all the blue/black/lavender/brown reds in a large laying flock. Am I correct in assuming that these colors can be mixed and eventually produce a combination of brown reds/lemon blue.
Brown red to brown red will give you brown reds. I've never bred lemon blue, but some
claim it is the same genotype as brown red with blue added (Bl/bl). I would try a brown red cock over a blue pullet to start with. Remember when you deal with blue you have a lot of wasters, like lemon splash and lemon black...unless lemon black (if the orange feathers aren't turned to lemon, what should be a lemon black would be a brown red).
Personally I think you would also need to introduce Ig (
Inhibitor of
gold aka lemon) to lighten the orange areas of the brown red to lemon. I don't know of an outcross, to another variety of Ameraucana, that will bring it in and you may have to cross to another breed with it. Lavender would dilute the orange, but also the blue and that wouldn't be the color you are after. Maybe forget the blue and go for a lemon lavender.