Just came across this great tutorial from Adafruit showing you how to can mod your IRIS to include cool LED's under the motors and some prop guards (less cool but definitely useful!).
The prop guards are 3D printed, and you can find the STL files here. The LEDs require abit more work to install, but they use the Trinket 5V microcontroller and 4x NeoPixel LED rings. The LED mounts are also 3D printed. Overall this is a well written tutorial that is easy to follow and has great pictures too, and ideal if you want to learn how to hack and mod things
You can read the full tutorial here