If the husband has one gene for blue and one gene for brown, and the wife has one gene for blue and one gene for some other color, statistically there is a one in four chance that a child will have blue eyes. Three out of nine is close enough since statistics and reality are not identical.
With two green eyed parents, they would each have a blue eyed gene, however, the green is much lighter than brown, and would contribute much less melanin, so perhaps some shade of blue might include a green genetic input. My husband had very clear light blue eyes. Our grandson has fairly dark blue eyes. I feel certain my husband was a pure recessive for blue, but I’ll bet our grandson has a little bit of melanin in his eye color. Don’t be suspecting infidelity based on your two cases.
LOL No infidelity here. I’m Mom. I think I would know.
But really hubby and I have grandparents/great-grandparents with blue eyes. Genetic expression is fascinating. :-)