I am thinking of using two shades of green for a small boy's room. It's smallish room but he's a small boy so not that concerned about ways to make it appear spacious etc but what are the "rules" re. using 2 colours on four walls? Three of one, one of the other? Half and half would look odd I think. We have one window wall opposite one door wall (long sides) and two short walls iyswim.