So you want to upgrade your existing pair of headphones with Bluetooth controlled NeoPixel LEDs? Adafruit has a guide for you. The Adafruit Bluefruit LE Connect app for iOS or Android lets you change the color of the LED rings and trigger animations.
You are going to need a Adafruit Feather 32u4 Bluefruit LE and a smartphone for the app to get started. The guide is available here.