What is the Difference Between a Common Gallinule, a Purple Gallinule and an American Coot?

Finally, I have seen a Purple Gallinule.  After the morning ride to Paynes Prairie, we took an afternoon drive to Leesburg Florida's Venetian Gardens City Park to see the Purple Gallinules.  Bill said we would have a 99% chance of seeing them and we did!  There were also a number of Common Gallinules (also known as the Common Moorhen) and American Coots.  So I thought I would put a collage together of the three of them who are obviously closely related.  The big one is the Purple Gallinule.  The ones in the upper right are the American Coots (this picture was from NC) and on the bottom is the Common Gallinule who is dark like the Purple Gallinule but doesn't have his striking coloration which even in low light was a brilliant blue/purple.

Here you can see the bright blue and aqua plumage as well as the coloration on the beak of the Purple Gallinule.

Here was another Purple Gallinule under the bridge.  If you look closely, you will see that he has one injured leg.  They have big feet like the Moorhens and the Coots.

 Here you can see the big feet!

A couple of the Gallinules were eating a dead fish on the side of the creek.

This is one of the Common Gallinules which has much duller colors for sure!