An arbitrary number of people are buried in the sand in a line and a hat is placed on their head (as in the previous puzzle Hats). Each hat is either red or blue, and there is no restriction on the total number of either color. Furthermore, each person can see the color of all the hats ahead of them, but are unable to see those behind them or their own. Starting with the back person, who can see all hats but his own, each person must call a hat color and nothing more.
If the whole group agrees on a strategy beforehand, how many people can accurately say the correct color of the hat they are wearing?
What strategy will they use?