Ha! It's an old illustrator trick going back to the days of Rembrandt. In the painting days, you just cover the entire canvas with blue and then paint in the warm highlights. In this particular 3D piece, I just pointed a blue spot light with the angular falloff set to 100% towards the snow globe. So, every place that the warm light doesn't shine is tinted blue; yet it turns darker the further away from the focus point it gets.