Start with true Ameraucana or Cream Legbars. Research for a breeder that has been producing nice colored blue eggs. From there, it's a matter of selective breeding. Breed the hens that lay the best colored eggs to a rooster that came from the best colored egg. Continue to cull for egg color. Don't introduce any white or brown genes to your breeders, you'll be chasing those colors out for generations.
Lots of breeders of those breeds have left egg color for last, going for refining the breed to the standard (or proposed standard) over egg color. That's why some of the nicer birds lay more pale or dilute looking eggs, they were bred for type first.