Light up colors in the dark !
Step 1:
Cut some colorful gel papers in the same size of the box opening
Step 2:
The shortcut is to put a gel paper on top of the light source, this way, you can create a colorful light and place it directly in the space box.
Step 3:
But we will do something more intricate.
Use permanent marker and draw over the stenciled shapes
Step 4:
Cut the gel paper along your mark
Step 5:
Paste them over the stencil cutouts. I used scotch tape.
Step 6:
Use any color you feel fits with the cutout shape.
Step 7 : 
This idea can apply to many themes.
Final Result :
The more colors, the more fun !