Co-dominant means that both indicators will be expressed when in a heterozygous organism.
So for the phenotype it will either be blue and yellow or it will be green which is the color you get when you mix blue and yellow but let’s assume in this case that it will be blue and yellow. Now when you cross a blue parrot who’s genotype is BB and a heterozygous parrot who’s genotype is BY, we use a punnet square to determine the possible offspring.
B B B BB BB Y BY BY
Therefore the genotype ratio is 50% BB and 50% BY and the phenotype ratio is 50% blue colored parrot and 50% blue and yellow colored parrot. Thus in this case both phenotypic and genotypic ratio are same i.e. 1:1.