Solution-Which outcomes are not possible

In fruit flies the gene for yellow body
April 24, 2020
Solution-Describe the three common shapes of bacteria
April 24, 2020

Solution-Which outcomes are not possible

Can someone explain how to do the following problem?

Feather color in budgies is determined by two different genes, Y and B, one for pigment on the outside and one for the inside of the feather. YYBB, YyBB, or YYBb is green; yyBB or yyBb is blue; YYbb or Yybb is yellow; and yybb is white. A blue budgie is crossed with a white budgie. Which outcomes are not possible?