Takeuchi TB015 cooling issue?

Hello today I noticed analog gauge on the console on the right side was running low in the white area and not in the green. THis was when I had the engine rev'd up. When I turned the throttle down to idle the needle bounced up into the green. Shutting it down I could see it was smoking some (not sure from where) and there was some antifreeze on top of the overflow bottle. I let it cool down and removed the radiator cap and its full. Replaced the cap and fired it back up and the needle did the same thing. At idle its in the green and as I rev it up it drops down into the white area. Before it would always run in the green reguardless of the engine rpm.

So what is this analog gauge indicating? I originally thought it was temperature but now I think its an indicator of the flow of coolant?

If not what is it indicating? What does this typically indicate?

Thank You

~ Phil