For most flashlight routines that I have used in class I use two or three colors.  I use a large permanent marker and color in the lens. Depending on the marker, you may want to let it dry and then color it again.

Instead of using permanent markers, you could use colored plastic wrap and rubber bands.  I didn't like how often my rubber bands disappeared and turned into weapons, so after a time or two I decided this was not a good choice for me.

I chose inexpensive flashlights from the dollar store about bought about 10 more than my largest class because I expected some of them to break easily.  The batteries were pretty expensive, but with the help of a regional grant I was able to get enough to fill every flashlight.  

When using the flashlights sitting down, you get a large light on the ceiling.  It's pretty, but not very distinct or clear if your room isn't completely dark.  In the picture above you can see what it looks like when students are sitting.  In the picture below students were standing.  That produced a smaller, cleaner look to their light and it looked much better when we were all working together.

You could always buy smaller flashlights with a stronger beam to get the same effect.

Before putting flashlights in their hands we listen to the piece of music.  We either follow a listening maps or we listen and create our own listening map.  This gives students the experience they need to be successful when they get the flashlights.

We label each section with a letter name and decide on an action for the flashlight.

This video is of one of my 5th grade classes and their first attempt at a flashlight routine to "Cantina Band".  This is an unedited, imperfect, completely authentic look at how this works in my classroom.  I love how at section D they are in awe of their own awesomeness!

I hope this inspires you to try using flashlights in your classroom.  Do you have any favorite pieces that would work well with flashlights?  I would love to learn about them.  Let me know in the comments.