Some images would look inversed if printed white on black rather than black on white; is that the issue here? This is especially true of things with highlights/chrome or certain elements that simply MUST be either dark (pupil) or light (white of an eye).
^If that is the case, I would keep the line art black and just toss it on top of a light-colored oval, or whatever. Maybe have a bit of the car hang over the edge of the oval, but do the same light color behind that extending out about 24px from the black art. Or you can make a copy of all the vector car art and set it to have a 48px white outline with the Behind Fill option, which nets to 24px; then place this behind the black car art, or whatever combination makes since for the art. I can sometimes apply the white outline Behind Fill directly to the black art, but sometimes you want just the outside outline so want an underlying shape that is only the outline of the overall art.