It is still possible to get it wrong. Let's face it, racism is so embedded in everyday life, no matter how self-reflective you are, there can be times when you just make a mistake. And then should apologise and learn from it, and do better in future.
Actually, when I think about how pervasive racism is, I would say it is difficult not to be racist.
DD's birth family (black South Africans) made a big deal out of her having lighter skin than her sister - it was seen as something to congratulate her on. And pretty nasty for her sister to experience. But then, they had been immersed in the racist narrative of pale skin being superior in every way. And taking it further, while DD had paler skin than her sister, she still had dark skin (and tight, curly hair) compared to people who weren't/aren't black.
Are DD's birth family to be condemned as racist as well?