Hey OP, considering that you're Asian and he's white, it could be that your fiance's parents like you just fine and that they believe, by their standards, that they are being warm and welcoming. They just have more reserve and more boundaries with family than you may be used to with your cultural heritage.
If your heritage is one where DILs, especially, are taken into their husband's family as their own, you'll probably find your in-laws distant by comparison.
My sister-in-law (Asian), married a white man, and she finds his family very reserved, and thinks they don't like her. I think they do, and they're treating her with the utmost respect and observing boundaries she doesn't even know exist in family.
I'm a white American, and my Asian in-laws have never accepted me, even after kids and almost 20 years living nearby. The ones who let down their guard have described the ways they have a lot of prejudice against non-Asian people. I've been unfailingly nice and pleasant, and I've smilingly put up with a lot of crap, but I have come to accept how things are.
Like another poster, my MIL is a terror, and she believes I've stolen her oldest son and turned him against her.