def color_conversion_function(start_type, target_type):
    """
    Decorator to indicate a function that performs a conversion from one color
    space to another.

    This decorator will return the original function unmodified, however it will
    be registered in the _conversion_manager so it can be used to perform color
    space transformations between color spaces that do not have direct
    conversion functions (e.g., Luv to CMYK).

    Note: For a conversion to/from RGB supply the BaseRGBColor class.

    :param start_type: Starting color space type
    :param target_type: Target color space type
    """
    def decorator(f):
        f.start_type = start_type
        f.target_type = target_type
        _conversion_manager.add_type_conversion(start_type, target_type, f)
        return f

    return decorator