The darker Khaki color apparently is fairly common in the Dun / Khaki Polish varieties, so if you search for White Crested Khaki Polish you can find a few pictures that show various khaki shades. This was a White Crested Khaki Polish at a show I went to:
View attachment 3629233
Compared to some of my Fawn (dun) Silver Duckwing OEGBs, you can see it's almost the same shade of gray-brown versus the Khaki SDW who almost looks white at first glance (he was still growing back his tail feathers from molting at the time I took that picture

).
View attachment 3629250
The lighting in the show barn was absolutely terrible in places so there's some wash-out in this picture, but this is about as true to what the dun version looked like in person as I could get. They referred to it as White Crested Chocolate, but then said when bred it produces some khakis and some blacks, so, you know, the forever super clear naming conventions for chicken varieties.