def _is_valid_color(colors :dict, user_color :str):
    """Returns true if user_color is a graph color provided by matplotlib

    Positional Arguments:
        colors : dict
            - dict of all colors supported by matplotlib passed in
            by the graph_colors decorator
        user_color : str
            - a string representing the name of a color
    """
    try:
        colors[user_color]
    except KeyError:
        return False
    return True