Of the four elements, what has proven to be the problem child? Earth. Who's supposed to get earth? In Alpha, Richard Garfield established that blue is the color of air and water and red is the color of earth and fire. The other three elements are pretty clean. Water feels very blue and fire feels very red. Air doesn't matter all that much as it's hard to illustrate objects made of air so we don't use air as much as the rest. So, red is earth.
But wait, isn't green the color of nature. What's more nature than earth? Doesn't green have elementals (like Maro) walking around that are comprised of earth? So earth is green.
But wait, aren't golems artifact creatures. And traditionally golems are made out of, you guessed it, earth. So earth is artifacts?
Just wait until one day someone starts exploring the agrarian side of white. Farming is all about dirt, right?