I have this weird (AKA bad) way of not counting cards like
sejiri merfolk and
dauntless river marshal (and similar) as gold cards, because while you do need the other land type, so you're technically playing that color, for the card's full effect, they CAN be played without them- before you draw the color etc, and my players already take dual lands highly, so even if they aren't playing white at all, they would take
Hallowed Fountain and
Arid Mesa and still play blue, so why not play those
sejiri merfolk? It just doesn't quite feel gold to me.