I think that World 4 has a darker tendency because it is the invasion hot-spot. So when someone dies in their human form due to an invader or dueling their WT goes blacker and so does the average for that world. But I have played with world 4 being almost pure white when the servers were slower and there was less pvp.
You should try a faith build Serious, out of the 4 chars I have made on DeS so far my melee faith support character is my favorite
EDIT: thing to make clear, the WT doesnt shift to an average once you start playing your save as soon as you load your game and start playing you are the only thing affecting your World's tendencies, It only shifts back to the average of many players after you relog, not during gameplay.