Button and backing case designed to fit a neopixel and 6mm momentary tactile switch button. As seen on the Adafruit Learning Center.
Full tutorial here:
https://learn.adafruit.com/3d-printed-neopixel-tactile-switch-buttons/introduction
This is the back of the button. The button cover is here:
https://www.shapeways.com/product/2FZANAKEA/neopixel-tactile-button-30mm-om