I exposed a black bottle cap by two light sources ( LEDs), one source is white and the other one is red as in the picture. I noticed that one penumbra toward the red light source is reddish in color which makes sense because this area is only exposed to the red source. What makes a puzzle is the other penumbra toward the white source is green. What is the reason? No green light source was in the room and the screen is a white paper.