Hello there!
Apologies if this post seems image-heavy, but it illustrates a point.
On Akril's
excellent Sierra Resource Files site, there are
several sketches extracted from the resource files of Inside the Chest/Behind the Developers' Shield from the KQ Collection. In particular, there are several pencil sketches for high-resolution character portraits in KQ6.
There's a portrait of Lady Celeste of the Winged Ones, which shows her much as she appears in the final game.

Left and middle: two versions of the Celeste portrait from the resource files. Right: Celeste portrait from KQ6 Windows.
She looks much like the Winged Ones do in general: human-style light skin tone, dark hair, dark irises. The Winged One gate guard looks very similar:

However, there are also sketches for dialogue portraits of Lord Azure and Lady Aeriel (which were eventually scrapped). These early drawings show the Winged Ones as having blank white eyes.


At top, two versions of Azure's portrait drawing; at bottom, two versions of Aeriel's, all from the Chest/Shield resource files.
Interestingly, however, the KQ6 hintbook features an alternate drawing for Lady Celeste's portrait. Here she has lighter hair and blank white eyes, like the early portraits of Azure and Aeriel.

Celeste's portrait sketch next to Azure's, from the hint book.
InterAction Magazine vol. 5, no. 3, from Fall 1992, also features
a black-and-white preparatory drawing for the background art of Azure on his throne, in which he appears to have blank white eyes as well.
What to make of this? Well....
I may be going out on a limb here, but, judging by the lighter hair of Celeste in her earlier dialogue portrait, I suspect the original intention of the Sierra artists may have been to make the Winged Ones resemble Roman marble statues. That is, they'd have marble-white skin and hair, and blank white eyes.
This would correspond to the Greek/Roman-inspired style of Winged One art and architecture as seen in-game in KQ6. In the final game, though, the Winged Ones look like actual people from Italy, as commonly stereotyped (light skin, dark hair, dark eyes).
Of course, I could be wrong (the portraits ARE black and white, and it's hard to tell for sure). But the Winged Ones DEFINITELY originally had blank white eyes, at least.
(Ironically, actual Greek and Roman statues were painted in bright, gaudy colors, which included the pupil and iris of the statues' eyes. It's only due to thousands of years of wear and weathering that the paint has come off those statues that survive today, creating a common misperception of what a Roman statue "should" look like.)