Yep I agree.
It would be one thing if they presented the vocabulary words in the context of a sentence, then reading the on’yomi is 100% wrong. But just seeing the same kanji with a different coloured background is really a pretty abstract criteria.
I understand the rationale behind on’yomi answers to vocabulary being immediately wrong, but it does seem like it’s too punishing - at least for the first few levels. It’s hardly if ever a problem for me anymore, you do get used to treating things with purple backgrounds as if they’re standalone words, but it is pretty arbitrary for the first while.

