Reddit mentions of Life along the Silk Road: Second Edition

Unfortunately I don't really know anything that specifically focuses on this aspect of Chinese history. Since it's most prominent during the Tang Dynasty (though you see it happening sometimes during other periods - for instance, an Emperor during the five dynasties and ten kingdoms period was notorious for supposedly having a thing for Iranian women and had many of them in his harem, among other apparently kinky scandalous things he did), so that's probably a good place to start. The main book on the Tang Dynasty that I've read is the one that's part of the History of Imperial China Series, which I've found overall to be a great introductory but academically rigorous introduction to the history of China in general - Amazon link to that here. I read the kindle version and there's one chapter on foreigners and foreign relations if I remember correctly. Right now I'm starting to read China's Golden Age: Everyday Life in the Tang Dynasty so we'll see how that goes.

The other place to look for would be books on the Silk Road. Susan Whitfield's Life Along the Silk Road was the first book I read in my recent binge on Chinese/Chinese-related history books, and it basically covers several centuries of Silk Road history through the eyes of 12 fictional individuals of different ethnicities and classes. Though fictional, their lives are drawn heavily from available sources. One of these individuals is a light-haired courtesan of Central Asian origin (or light eyed, kinda forgot but point is she'd be foreign in China), who lives much of her life in Chang'an, so the chapter on her might be of interest. The other Silk Road book I'm about to read right now is The Silk Road: A New History, so we'll see how that one goes.

I'd probably recommend getting Whitfield's book and then looking up the sources she uses. Unfortunately, these sources I mentioned above don't really go into much detail about the dynamics of these potential inter-"racial" sexual/romantic relations (I use racial in quotation marks of course because our modern conceptions of race would not be useful in analyzing this historical context) other than the fact that it happened and some Chinese guys wrote some "dood dem blonde grills r hawt" literature, but maybe there might be some shorter articles or research papers available that do focus more on them.