Set white coloured theme of an rgb bulb.

        Args:
            brightness(int): Value for the brightness (25-255).
            colourtemp(int): Value for the colour temperature (0-255).

def set_white(self, brightness, colourtemp):
        """
        Set white coloured theme of an rgb bulb.

        Args:
            brightness(int): Value for the brightness (25-255).
            colourtemp(int): Value for the colour temperature (0-255).
        """
        if not 25 <= brightness <= 255:
            raise ValueError("The brightness needs to be between 25 and 255.")
        if not 0 <= colourtemp <= 255:
            raise ValueError("The colour temperature needs to be between 0 and 255.")

        payload = self.generate_payload(SET, {
            self.DPS_INDEX_MODE: self.DPS_MODE_WHITE,
            self.DPS_INDEX_BRIGHTNESS: brightness,
            self.DPS_INDEX_COLOURTEMP: colourtemp})

        data = self._send_receive(payload)
        return data