My first step in turning a white vehicle into a black vehicle.

Changing the color of a white vehicle to black is the worst.

Its all about reflections and I tried to use the existing ones in the white.
I cut out with the body shell, duplicating it and processing it with curves or levels to turn the darkest 'whites; into very dark gray and the lightest 'whites ' into somewhat lighter darkish colors or tones as appropriates.
At that point it was flat and I duplicated that layer and processed those two with differing localized contrast enhancement (camera RAW clarity +fiddling and a Topaz clarity to taste) striving to accentuate those tonal changes.
I had a nose + the rest of the car then and processed another middle layer for the side door insert with the interesting reflection. That's actually overlaid by changing transparency.
This is V1 and I ended on V11 but the essence of the project is already here. The ensuing saves were cleanup and adding more substantive but fake reflections, The burn tool was my friend and used a lot.