Half of the total number of Opals children (50%) will have blue hair.
Explanation:
When an Oompah with purple hair (Pr) marries an Opal with blue hair (rr) out of the four children born two will have blue hair as represented by the below table.
From the table we find that two children are born with the dominant (purple) trait and two with the recessive (blue) trait. Allele is the other word for trait defined by Gregor Mendel in his Law of Segregation. Dominant allele is visible and recessive allele is masked.
