Cool mod. I'm doing it too. Thank you for figuring it out. I never put them in the car yet. They have clear plastic on the inside so I see why you had to change the color. The original knobs seem to be on real tight. How did you remove them? Instructions on box say to use a piece of cloth with pliers. Is it that easy?
These can be ordered with a red surround instead of black too. The red ones come with a red plastic on the inside. Red surround wouldn't look right though but the red inner plastic part would match the color of the back lighting.