I have a horse. Do you know what color it is? Allan said, "I guess it is not black". Brian said, "It is either brown, or gray". Charlie said "I know it is brown". I said, "At least one of you is right and at least one of you is wrong." What is the color of my horse if the color is one of the above?

This is a logical deduction problem. If the horse were brown, both Brian and Charlie would be right, violating the condition that 'at least one of you is wrong'. If it were black, both Allan (who said 'not black') and Brian (who said brown or gray) would be wrong, violating 'at least one of you is right'. Therefore, it must be gray, making Brian right and Allan wrong.