You will get a more even blue if at least some of the blue is applied in thin sprayed clearcoats, depending on what effect you are looking for. Since the amount of shellac you are applying is not much, the color should not be affected significantly.
A thin coat of shellac can work well as a pre-stain conditioner, to help with more even stain absorption. Technique is so much about exact specifics and details. Give two people the same materials, you could easily get two different results. Best would be to test your method before doing it in real time. That will give you an idea of what you are up against. If you need to test it a few times, or over the course of a few days or whatever, so be it. Knowledge is power.
There are numerous different ways you could do this. Some are better than others.