Created a fixture with rgbw. In 2D Monitor not shown white. With yellow or amber also tested. Not shown.
White with rgb made , in 2D view ok. Standalone w shows black with flicker as it would show something.
Edit : it's a generic LED lamp with extra white LEDs. Made as other try a two head fixture. One side RGB with dimmer , other side white with dimmer . In 2D Monitor first head ok, second shows directly white without channel on.
Regards Ralf