@malik basha,
Since you see two green dots, you know at most there can only be one red dot. That red dot would be on your forehead, but it also could be a green dot at this point.
Now, here's the tricky part, and I'll do my best to explain it. The answer is in the fact that you have to now put yourself in to the mind of the other players. I'll label the two other players Player 1 and Player 2.
So step inside player one.
There are three options he can see.
Option 1. Two red dots
Option 2. Two green dots
Option 3. One red, one green
For option one to be valid you and player 2 need to both have red dots on your head. You can see that player 2 does not have a red dot on his head. So option 1 is impossible.
For option 2 to be valid you and player 2 need to both have green dots on your head. You see player two has a green dot, but you're unsure what you have. This option has the possibility of being true.
For option 3 to be valid you need to have a red dot on your head, since you see player 2 has a green dot.
So as of right now you are able to take out option one, and are only left with options 2 and 3. Here's the real meta part. Go back into player ones head. He doesn't know the answer. He's wondering if he has a red or green dot on his head.
So, Now compare what he's thinking to the options that are left.
Option 3- there is one red dot and one green dot. You would have the red dot, player 3 would have the green dot.
Compared with
Player one's uncertainty of having a red or green dot. If he had a red dot on his head, and you had a red dot on your head there would be two red dots. Since at the beginning we deduced that there could only be one red dot this makes option 3 invalid.
Option 2 is the only option left. YOU HAVE A MOTHER ******* GREEN DOT ON YOUR HEAD!!!!!! HOLLA!!!!
Love,
Ebuni