Breeding Alexandrine Mutations: Blue & Grey
In order to achieve a visual blue or grey, both parents must carry the blue gene as blue is a recessive mutation. Breeding a blue/grey is therefore more complicated than breeding a lutino. I don't have first hand experience of doing this but from my knowledge of genetics and extending what I have discussed in my article on the lutino, I would suggest the following.
Start with 2 pairs, all birds should be unrelated.
Normal Alexandrine cock X Blue IRN hen
Normal Alexandrine cock X Grey IRN hen
Pair one will give you offsprings all of which are split to Blue. The good news is that you can use both males and females from here in step two.
Pair two will also give you offsprings all of which are split to blue. If your grey IRN was single factor grey then half of the offsprings will appear grey-green. If the Grey IRN was double factor grey all the offsprings will be grey green. You should use a grey-green from this pairing in Step 2.
You have 2 options here, both are equally good and your choice should depend on what offsprings look best and what is available.
option 1: Green/Blue cock from Pair one X Grey Green/Blue hen from Pair two
option 2: Grey Green/Blue cock from Pair two X Green/Blue hen from Pair one
This pairing should give you a visual blue and a visual Grey bird along with some grey-greens. The probability of getting a visual Grey or blue is 25% so you may have to try a few times before you get the desired result. You may also setup more than one pair in this step from birds of step 1 to expedite the program. The green and grey-greens produced here may or may not carry the blue gene. Since there is no way of differentiating between the two, it is best to not use the greens produced here.
Step 3 would look like step 1 except you will now use the 2nd generation Blue and the 2nd generation Grey instead of the IRNs. Step 4 would be similar to Step 2.