No, vannak (plural 3rd form) cannot used in this sentence. When it is about describing a property, the substantive verb does not necessary in present tense. E.g. ő katona ((s)he is a soldier), az ég kék (the sky is blue), a bankok régiek... But in the past and future tenses the substantive verb is required: ő katona volt ((s)he was a soldier), az ég kék volt (the sky was blue); ő katona lesz ((s)he will be a soldier), az ég kék lesz (the sky will be blue).