What do the rings around the Pokemon indicate?

[iMore Question]

When trying to catch a Pokemon, they sometimes show different sizes and colors of rings, what do they mean? Seems to me it indicates how hard they are to catch but I'm not sure.

 

[iOS Gravity]

It's giving you a read of how precise your throw will be if you throw it when the ring is green

 

[metllicamilitia]

Green means easy to catch, yellow is somewhat difficult to catch, and red is hard to catch. The smaller the ring is when you throw your pokeball the greater your chance of catching the Pok?mon is. I have found though that with the small ring when you throw, you need to be more accurate and hit near or inside the ring.