Thanks for responding. I initially left the ILL wire from the Seicane harness disconnected and the HU dimmed with headlights as expected, just wouldn't change the light color of the buttons. When contacting Tech Support they insist that needs to be terminated with factory ILL wire which is non-existent from factory at the PCM. Not sure they're hearing that this is CAN bust and MOST. Maybe it's a defective CAN bus decoder or in the HU. My old PCM died which was reason for doing this. Thought your install may have made you do something with this wire.

The illumination wire should get 12V when the car's headlights are on and 0V when the headlights are off; this tells the head unit to go into night mode and dim the screen. I would think that information gets to the head unit via the CANBUS but I will have to check the wiring diagram and/or check with a multimeter. Whether or not this information is relayed via CANBUS may also depend on whether or not you have automatic headlights. Are you using a CANBUS decoder? Do you have automatic lights? You are mentioning button color but I am not sure which button you are referring to. Do you mean the screen background color?