not me apparently.

I'm really pissing annoyed that I can't work this out..I feel really stupid.

My friend told me this riddle last night and I still can't work it out, I'm gonna tell him I don't know the answer but do any of you:

4 guys are going to die, they've all had a hat put on their head. If they can say what colour hat they have on their head then they can live. Only one of them can do this which one is it?

set up is as follows:

x I o x o

x = guy in black hat
o = guy in white hat
I = a big massive fuck off wall between them that can't be seen through, round or over.

all the men have been told to face forward towards the wall so can only see those people in front of them, they can't look up down sideways and they can't talk. they know how many people there are in total, how many people are behind them and they know that there are two hats of each colour.

which one is it?!!