The captain knew about the difficulty distinguishing the cloud from the ice. On hearing of the low cloud layer over McMurdo Station, he considered baling out and going elsewhere.
The condition known as whiteout, it's insidious nature and its rapid onset were virtually completely unknown in commercial aviation, particularly at ANZ in 1979. Of course Capt Collins understood the difficulty of distinguishing between snow and ice, as would the other crew who flew those sightseeing sectors, but that in itself is completely different to the condition of whiteout phenomena.