def is_rgb(value):
        """Check for valid RGB tuple value.

        Parameters
        ----------
        value : iterable of length 3 (e.g. [255, 0, 0])
            the value to be checked

        Returns
        -------
        valid : bool
            whether the value is valid or not

        """

        if not len(value) == 3:
            return False
        elif False in [isinstance(x, int) for x in value]:
            return False
        elif False in [0 <= x <= 255 for x in value]:
            return False
        else:
            return True