What are the rings around Pokemon when trying to catch them?

[AC Question]

They started off green but as I've been playing they've changed colors to like orange and yellow. What do they mean? I thought it meant they were more powerful Pokemon but that doesn't seem to be it.

 

[chocoeatstacos]

They started off green but as I've been playing they've changed colors to like orange and yellow. What do they mean? I thought it meant they were more powerful Pokemon but that doesn't seem to be it.

From what I've gathered it might not necessarily mean the pokemon is more powerful, just that it's more difficult to capture. I know I didn't start seeing the yellow rings until the cp were up in the low hundreds, meaning in a sense ya the pokemon is more powerful than a lower cp level version of itself.