Choosing a Watermelon
The part of the watermelon that sits on the ground and leaves a pale patch that never sees the sun, had turned a pale butter yellow. Unc says if that patch on which the watermelon grows against the ground is white, then the watermelon is not at the peak of ripeness.
The fact that our growth patch had turned a pale buttery yellow was a good indication of sweetness.
Oh, and when you thump it, the best ripeness should have a sound in a lower register that resonates. A higher pitched thump that turns into more of a thud with no resonance is a watermelon not at its peak of ripeness.
Read more here.