Caps

Four youngsters enter a contest.

In a room, they were made to sit on the chairs arranged in a particular fashion.

There was a opaque wall.

A single chair was kept on the one-side (say X) of the wall and other three chairs were kept on the other side (say Y) back to back in a line.

Remember that all the chairs are facing the wall.

Now, the lads were asked to occupy their seats.

'A' occupied the chair kept on the 'X' side of the wall.

Now comes the 'Y' side of the wall....

'B' occupied the 1st chair kept on the 'Y' side of the wall.

'C' on the 2nd and 'D' on the 3rd chair.

Later, a cap, either red or green, was placed on the head of the each guy.

The guy doesn't know which colored cap is there on his head, but he could obiviously see the color of the cap placed on the guy's head seating in front of him.

Task was if anyone guy could tell the color of the cap he's wearing the team wins .

A guy did and they won the prize.

Now, here is the question.

Question: You have to tell me who's that guy and how was it done?

if :

>A had red

>B had red

>C had green

>D had green cap

They were told that there are only four caps, two red and two green.

[Post your answers with explanation in the comments]

Image Credits: highsnobiety.com