+rep for that? What? Players have bashed CA since time immemorial for that

color scheme

I don't know what they put in their coffee, but it's obviously some quite hardcore stuff.
As for why Hungary isn't liked, the color scheme does have an impact. But I think it comes more down to uniqueness.
Every faction is unique, but some are more similar than others. Hungary loses out because of similarities. It is different from Poland, Russia and the Byzantines, but those factions added together have all the things Hungary has, and offer more entertaining campaigns.
As for other not-all-too-unique factions, they still have differences and offer good campaigns. Take Portugal and Spain, they're damn similar, and have pretty similar campaigns, but they're different enough right off the bat to warrant both some love. Hungary doesn't have a fun enough campaign, and when it loses uniqueness and is given that horrendous color scheme, it falls from grace.