Great work Adrian!
Your first example shows the white car, however the illustration was flat looking and didn't show the the form of the white surface, on the other hand, your second revised version using shadows, is much better, using shadows to show the form and texture of the white surface. Much more realistic!
Being a student of Dean Collins, the great photographic lighting master, and attending many of his seminars, he explained, it is always hard to illustrate black or white products, and make them look 3 dimensional. The key for white products is the use of shadows to bring out the from and texture of a white product (car), and for a black product (car), the trick is to use specular highlights to define shape and texture.
Dean Collins came up with a concept in photography, he called
"3D Contrast" too explain how this works and how to capture different color objects and make them look 3 dimensional, using Specular Highlights, the Diffused Value, and Shadows. Below is a short video of Dean at one of his seminars explaining his 3D contrast principle. I have been using his 3D Contrast principal in my commercial photography ever since leaning it in the late 80's.
http://www.youtube.com/watch?v=bYM6cQYgEgk&feature=mfu_in_order&list=UL