Back in December I did this to my Leaf on an obsessive DIY binge. It's still working three months later, I'm planning on buying more LEDs to redo the bottom strips, but haven't had time or money.
It looks purple in this photo, this is an iPhone effect. The true color is blue.
I've been wanting to share, but had problems initially with cheap LEDs (in series) going bad and really haven't been able to utilize the underglow affect since 2 weeks after I installed them. The charger LEDs only worked for the first 5 inches or so. I believe stretching them and bending them during the install ruined these low quality waterproof strips.
I designed 3D printed clips to make this happen.
They can be downloaded here
The brains of the operation is an Adafruit Trinket (Arduino), and a PWM enabled 12v power supply. The power supply is connected to the 12v battery (fuse in wire) and passes 5v to the Arduino.
Download case here
Two PWM pins from the Arduino go to the PWM pins on the 12v power supply. I've programmed the Arduino to pulsate while on, a smooth "breathing" effect. The Arduino quickly fades the lights on when the charging port switch presses the tactile button, completing a 5v connection to the Arduino's input pin.
Download switch here
I'll post more pictures and maybe some instructions/part list when I have a fully working setup