We eat these a lot in Australia. 6 inches is way too big, they should be eaten as tender squash. They can be any colour from white to green to bright yellow. Pick them when they fit in the palm of your hand or a little bigger. Cook as courgettes. The more you pick, the more they grow. They can be slow to start and tend to have spurts where they will suddenly have 6 or 8 fruit :-)
They are nice quartered and steamed, or sliced and pan-cooked with garlic and chives. You can do anything with them as you would a courgette, their flavour is slightly different, a little more of an earthy flavour. Personally I love them, I grow the yellow ones which I think are called Sunbeam.