As for dark morphs if you start working with the albino gene the darker the morph or even a dark female the higher contrast the albino will be.
As far as hold backs you kinda have to look ahead and see what you want to produce. If you for example want to work toward producing bees,pewters,fire flies you will hold back more of your pastels so you can breed for all those in one season instead of only having two pastels and one year breed for bees and pewters and have to wait for the following season for you fire flies.