Italian, my experience of Swedish racism is that it certainly does exist, like it does here, but it is more tied to language and culture than to physical appearance. At least when I was a child, somebody who looked like a Swede but spoken broken Swedish or with a foreign accent would be far more likely to experience racism than somebody who looked totally different but spoke with a native accent and appeared au fait with Swedish cultural norms. Swedish racism in those days at least was more about xenophobia (will they know how to behave like us?). So a Finnish or Greek immigrant might expect to have a harder time than a Korean or Indian adoptee. I don't think my brother has experienced much racism, but I know my best friend who was the child of Finnish immigrants did occasionally. And as far as I am aware, the greatest sufferers from racism in Sweden today are Somalian immigrants, and to some extent Middle Easter immigrants. It's not something I would expect to touch the lives of my nephews.
Another factor that might have made a difference in those days (though possibly not now) would have been that there were hardly any adult immigrants from the countries which furnished the adopted children: so anyone with xenophobic tendencies who saw a Korean or Indian teenager around in the 70s would assume that s/he was adopted and therefore "one of us".
Lilka, as far as I am aware there are very few domestic adoptions in Sweden. Partly, I think, because there are fewer unwanted pregnancies: more take-up of contraception, plus an unwanted pregnancy would be more likely to end in abortion.
The first big wave of inter-racial adoptions in Sweden was in the 60s- so those children are now grown up and have families of their own.