I made a neopixel lightbar controller to add color to my macro photographs. I usually just use mono colored LEDs to accomplish that, but thought something like this will give me more control.
The design uses the Adafruit Trinket M0 as the main controller. The light bar is an Adafruit RGBW Neopixel stick. I used four potentiometers to control intensity of each color (Red, Green, Blue, and White). By varying the individual pots, you can create a multitude of different colors.
Detailed tutorial available here: https://github.com/mohitbhoite/neopixel-lightbar