How does the vocabulary highlighting feature work? Purple words

I’m turning on spanish subtitles (so now I see Spanish subtitles + English subtitles underneath)

I don’t understand, why are some words purple? Why aren’t the corresponding English words also labeled purple so I can see which correspond to which?

Was wondering the exact same thing, did you figure it out?

Hi, purple words are words that are above your knowledge level (you can select it in settings), so you could ignore them and just concentrate on white words. And grey words are names etc.