If the turkeys flush red that means they are excited.
Could be scared, could mean happy, I say it usually means they are happy.
I have two that look like red light bulbs when they see the feed bowl come out of the bag.
Its also a great indicator of if your turkey is sick or just sluggish. They dont flush nearly as much and stay a more pale shade at rest if they are sick. If they are just a little under the weather or finally turn for the better you'll see that hard red flush come back to them.
Even in the extreme heat (like Florida) just panting away and drinking water they will still flush when happy.
If they are young its a good way to sex the bird. The male will flush much deeper in the lower neck, the wattle under the chin, and around the beak. However this can also depend on breed. I've only had experience with what look to be Black Spanish mixes. As I always say, breeds are different once you cross the Pacific.