"Red against blue."
Translation:Κόκκινο εναντίον μπλε.
Why can't I use κατά here? It says that κατά means against, so why is it not correct?
Its usage is different. It cannot be used in syntax "A vs B".
However, you can use it in sentences like "The war/battle/etc. against B": "Ο πόλεμος κατά του μπλε" - "The war against blue". Note "μπλε" in genitive case and with definite article.
Same meaning, different preposition, different syntax: "Ο πόλεμος ενάντια στο μπλε".
Hi, Katharina -- My understanding is that εναντίον demands the genitive case. But you can't really tell, in this case, since μπλε is invariable, just like γκρι. Best wishes, Paul