How is it possible to explain one parent with black hair, one parent with brown hair, and a kid with blonde hair

The parents had traces of blond genes that werent as dominant

Explanation:

I put the punnet square below

the lowercase b is blond

we would need to see the picture to answer it

the offspring would all be white. if the parents are both white flowers then they have the genotype rr, which when crossed results in an all white punnet square.