That is a very good suggestion.

While better than anything I came up with on my own, I'm not sure that antonym is a perfect fit though.

For one, while hot/cold works, I'm not sure that red/green works.

Plus, antonym has a different connotation - it is the antonym of synonym. Antonym implies a word with the "opposite" meaning, not a concept with the "opposite" meaning.

I wouldn't be comfortable talking about the antonym of a concept.

Does anyone know if there are any languages that don't have this problem?