What does a yellow status indicator(the ball) mean in chat list in gmail?

Question

I mean chatting through gmail.

Answer 1

the person is online but unavailable

Answer 2

are you talking about the indicator next to the person's name? when you are afk or minimise or don't do nothing to the chat page for a while, the green indicator will become yellow, just like to say "away"  

Answer 3

green means available, yellow means idle, red means away.

if you dont know what idle is it means that the person is signed in, but hasnt been on their computer for like 10 min or more