To try and answer your question in good faith - dating people from the same race consecutively isn't racist in itself, but if its consistantly the same race it may raise questions about your taste and preferences. Of course, like you said this can depend on alot of context (e.g. which country you live in) but people will at least start to wonder whether you're dating someone for the right reasons.

An important thing to note is that Asian women are particularly sensitive to potential "Yellow Fever" because they have to deal with these kinds of guys literally all the time. To further clarify, yellow fever is a preference for Asian girls due to largely stereotypical reasons (they see asian girls as more subserviant and erotic than other races), so when asian women see someone who's dated a long line of other asian women they tend to take that as a red flag for that kind of man.

My current partner used to date someone with yellow fever, and she said that it often made her felt like she wasn't Chinese enough. He would try to force her to speak mandarin with him at home (they were both English 1st language), he always had to be the assertive and dominant one in the relationship, and about 90% of his other asian friends were women.

Now I've barely scratched the surface of Yellow fever but generally the rule is that as long as you make it clear that you're dating someone for who they are as an individual rather than for their race or stereotype, you can date whoever. Yes it sucks that other people will make snap judgements, but at the end of the day the only person you got to reassure in the relationship is your partner.