The problem with many (not all) of dating expats is that they are exploiting a power differential that exists between themselves and their partners. That may not be explicitly racist, but it is colonialist, which is a racist policy. Are they explicitly racist, i.e. do they do the slanty eyes thing and go around saying 'bing bong ching chong.' Nah. But are they good people? Eh, I guess it depends on your definition of good. I would say, not really in this moment, but maybe they can change.
This is very complex topic as far as what constitutes as colonialism. You're absolutely correct that there may exists a power differential when it comes to an expat (white guy) with an expat package (getting paid western middle class wages) while dating an Asian woman in an Asian country, but is that due to money and/or race (white privilege)? But, I also want to point out the nuance of that a money differential exists everywhere, in every country, so, it's not an expat exclusive thing, so I'm not sure how big of a factor when it comes to colonialism.
I'll just take a step by step approach on the topic and maybe I can make some sense of this for myself.
If we are to to hypothesize a stereotypical expat dating a lower SES woman, then that might be consider colonialist situation. But, is this a true colonialistic relationship? Is this relationship based on money? Who knows, but to assume that it is would dismiss the agency of the woman, so let's focus on the social side of it. What is the impetus of the social difference? Is it due to Hollywood's influence on perpetuating white status? I honestly don't know, but these countries also has their own media conglomerates where the main TV and movie stars are Asian, so I'm not sure how pervasive Hollywood's influence can be, especially in countries that were never colonized, like Thailand for example.
Let's hypothesize an expat dating a high SES woman, would you call this a colonialistic situation? I have trouble considering this one since money is not a power differential, and it's also possible that the woman has more wealth than the white guy (I know a few instances of these types of relationships). Is the social power differential also applicable in this context? Maybe, but it might also depend on which country we are talking about, for example, the Dutch colonized Indonesia, but again, Thailand never was.
So, in the end, I'm not sure how strong of an argument can be made about colonialism, because there are many variables that needs to be considered.
1). You're going to have to dismiss the agency of the Asian person, meaning, he/she is not dating the westerner due to simply liking them, but because they are doing it because of the money.
2). Each country has a different history with colonialism, and it may or may not be relevant.
3). The penetration of Hollywood pushing the white protagonist, and how much influence this has.
I still think it's much more nuance than what you're suggesting and it's a very reductive and too simple since humans have many reasons to date one another. But, to suggest that expats don't take advantage of their whiteness privilege is also denying a reality.
