That's a good catch with the Middle Eastern bit.
Unfortunately I don't have my books accessible to go quote hunting, but, using the wiki (which lacks descriptions of many important Daru figures, such as Murillio and Challice), it seems that the Daru people possess quite a bit of variation, with black-haired and blue eyed
Crokus and
Coll,
Rallick and
Torvald possessing at least black hair, with Rallick also being, relatively, "dark-skinned,"
Sulty (though the wiki doesn't clarify whether she is Daru) has blonde hair, while
Delish has light brown hair, pale skin, and brown eyes.
So it does not seem like the Daru can be classified as either uniformly Aryan or Middle Eastern (interestingly, according to wikipedia,
blue eye colouration is not uncommon thoughout the Mid East all the way to Central Asia and India, even, being most prevalent in the Levant countries, Iran, and Pakistan/Kashmir), but rather are more likely to be, as you say, the result of the relative "melting pot" that is Darujhistan, where the original Daru (descended from the Kindaru and their relatives) settled and most likely intermixed with the native Gadrobi as well as other peoples (the Rhivi and Nathii perhaps).
Perhaps thinking of Darujhistan more along the lines of a Genabackan Istanbul might thus make sense?
"But I saw you [Snake]…faced by Anomander [Mandy] himself. How did…"
"I escape? Well, I dazzled him with fancy words, edging ever closer, then used my ninja skills to strike like a cobra, knocking the sword [Spamnipur] away and drop-kicking him over the side before tumbling backwards, slaying another Piss'd Andii on the way."
Silence. Lots of silence. "Fine!" He shrugged and grinned, "Someone hit him in the face with a coin, and he cursed just long enough for me to get away." ~ Excerpt from Gardens of the Tea Spoon