Crown Prince squash going yellow.

One of my Crown Prince squash, which I harvested a few days ago, seem to be starting to go yellow. I'm pretty sure the irregular yellow patch wasn't there before and in fact I think none of them were yellow even when young. Does this mean it's going 'off'? The yellow area feels just as hard as the rest.

Is this a bad sign?

Thanks.

Thanks. My first time growing squash.