A New "Colored Hats" Problem

Three subjects—A, B, and C—were all perfect logicians. Each could instantly deduce all consequences of any set of premises. Also, each was aware that each of the others was a perfect logician. The three were shown seven stamps: two red ones, two yellow ones, and three green ones. They were then blindfolded, and a stamp was pasted on each of their foreheads; the remaining four stamps were placed in a drawer. When the blindfolds were removed, A was asked, "Do you know one color that you definitely do not have?" A replied, "No." Then B was asked the same question and replied, "No."

Is it possible, from this information, to deduce the color of A's stamp, or of B's, or of C's?

(Source: The Lady or the Tiger: And Other Logic Puzzles by Raymond Smullyan)

Well, to start with, it is not possible that both B and C have red or yellow stamps on their foreheads. If they did, then A would know that he does not have either a red or yellow stamp on his forehead. Now here's where things get tricky with meta-reasoning: it is not possible for C to have a red stamp on his forehead. Why not? Because, if C did have a red stamp, then B, having heard what A said, would know that he does not also have a red stamp on his forehead. The same goes for the color yellow. Therefore, C's stamp is green. (Nothing can be deduced about the color of the stamps of A and B.)