Synonyms that are in the dictionary are marked in green. Synonyms that are not in the dictionary are marked in red.
Antonyms that are in the dictionary are marked in green. Antonyms that are not in the dictionary are marked in red.
This is because you can actually look up lyrics to a song in the Search bar.
Source: https://www.slashgear.com/1333143/top-apple-music-hidden-features/