white lines on the veins of zucchini leaves
This problem isn't on all my zucchini plants, and they are flowering and apart from the white colours look relatively healthy.
Certified GKH Gardening Expert
There are many varieties that have a recessive trait for white veins, but there are also some conditions that may cause this as well. If it seems healthy, then it could likely be a trait of the plant.
I am including an article on plant diseases but none of them sound like what you are experiencing. I would watch it closely for any more symptoms.