I checked your site on when to pick a watermelon and it said many different things. I picked my watermelon when I could do the test you said, by it sounding hollow and the spot on the bottom was yellow, etc. But when I cut the melon open, it was just a white in color. So how do I know when it is ready and did the white mean I picked it way too early or what?
Certified GKH Gardening Expert
The flavor will be the real determinator on this, but it does sound like it was picked a bit early. Make sure that when you pick it, it feels heavy for its size. If the flavor is good on this one though, you may have planted a yellow fleshed watermelon, which can have an almost white flesh at times.