Christmas Lights + Magic Finger

You tell the children that you have drawn them a special Christmas picture, displaying a solid white silk handkerchief. You claim that it's a picture of a snowstorm! Sensing the skepticism from the crowd, you get the children to draw you a Christmas tree in the air as the handkerchief is dropped into a bag. When you remove the silk from the bag it now has the outline of a tree printed on it-but what a pity, there's no color! Different colors collected from the children's clothing then magically appear on the tree-but what a pity, there aren't any decorations! The silk is again dropped in the bag and you start plucking little red lights out of the air, dropping them into the bag as well. When the silk handkerchief is taken out, little red stars are covering the tree!