All you need is:
an old 5 watt flashlight
a glass tube from a florescent bulb
a small circular mirror
a case for a large toy lightsaber
a glass cutter
First you unscrew all of the screws and take out the lightsaber part leaving just the hilt.
Cut out a square of whatever color you want big enough to cover the top of the flashlight and use the tape to stick it on.
Put the flashlight in the hollow lightsaber hilt and tape it in place. Make sure you take out the red button on the lightsaber and the flashlight's switch is lined up with the hole that is left when you tape it in place.
Unscrew the ends of the florescent bulb and only save the tube and use enough tape to hold it in place.
take out the mirror part and use the glass cutter to cut it into the right size to fit into the tube. Tape it to the end of the bulb.
click the button through the hole and the colored light from the flashlight will shine up the tube and be reflected back down.