My Hat Is Off To You, Sir

Today's puzzle:

Four guys are in prison. Let's call them prisoners. The guard in charge of watching them decides to play a game with them. He puts one of the prisoners in one cell, and the other three in an adjacent cell. He then lines up the three in the one cell so that they are all facing the same direction. Next, he then takes four beanies, (two white and two black) and randomly puts them on all of their heads. The guy in the back of the three person line can see the color of the two beanies in front of him, (but not his own), the guy in the middle of the line can see the color of the guy in front of him, (but neither his own nor the guy behind him), and the guy at the front of the three person line, and the solo prisoner in the other cell, cannot see anyone's beany. The guard then tells them there are two white beanies and two black beanies, and if anyone can guess the color of his beany within the hour, he can go free, but if he guesses incorrecly, he will be shot. They are allowed to answer in any order, (as soon as they know, they can shout it out). If they say anything other than black or white within the hour, they will also be shot, (so no cheating). They only have 1 year left in jail, so assume that unless they know for sure, they won't guess, (they'd prefer to stay in jail for a year rather than get shot). Sooooooo...assuming they are all logical people, who, if anyone, will ALWAYS go free, (not matter what the distribution of hats is). The correct answer could range from no one to everyone. Good luck.