Question

What's the difference between black and white watermelon seeds?

Answer 1

The difference between white watermelon seeds and black watermelon seeds are that white watermelon seeds are not fertile and will not grow any watermelons if you planted them.

The black watermelon seeds are fertile and will grow watermelons if planted.

In short the white watermelon seeds are just not fully developed watermelon seeds and are immature and haven't developed into black watermelon seeds.