It's easier to understand White Duck when you compare it to other shades of white, like Sherwin Williams Shoji White.
Though very similar (and both super versatile), White Duck leans a bit more beige, while Shoji White can show a hint of green.
With a higher LRV (light reflectance value) of 82, SW Alabaster is quite a bit brighter than White Duck. Both colors are off-white with varying hints of greige.
When you compare them side by side, White Duck reads as darker and more beige.