The upgraded countdown timers on TNA pinball have cool interactive LEDS but I didn't like that they were just plain bright RGB leds. I printed these out of translucent PETG and used a dab of hot glue to attach them to the black frame that the timer mounts to, this diffused the RGB light as shown in the pics.

Initially printer at defaults (15% infill) but then printed at 100% infill which seems to diffuse the light better, but since they are short prints  you can try various infill settings and choose yourself.