Besides watermelon

That's true, I guess because of the peel. By that logic watermelons would have to be blue, though.

I was thinking that it's about composition (watermelon is mostly water), so probably more capsaicin. Hot like a pepper but big and round. And maybe some orangish bioluminescence too, since it's a made-up fruit and I'm allowed some creative licence.

Windmelon would then be very light and spongy.