Return a new instance from an RGB color hex string like ``'3C2F80'``.

def from_string(cls, rgb_hex_str):
        """
        Return a new instance from an RGB color hex string like ``'3C2F80'``.
        """
        r = int(rgb_hex_str[:2], 16)
        g = int(rgb_hex_str[2:4], 16)
        b = int(rgb_hex_str[4:], 16)
        return cls(r, g, b)