def placed_positions(hex_board, color):
    """
    Retrieve all positions on the HexBoard where the given color has
    placed a piece.
    :param hex_board: HexBoard Class for game-logic
    :param color: int HexBoard player color
    :return: list of all positions on the board that belong to color.
    """
    return [(i, j) for i in range(hex_board.size)
            for j in range(hex_board.size)
            if hex_board.is_color((i, j), color)]