When I was in college, My major was in advertising design. When you work in design, you learn a lot about color theory, or, in other words, the way that different colors relate to one another.
Satoshi, your celica is mostly red and black, I would go with the red neon, as it maintains a much cleaner look overall, the blue is a good contrast, and would not be out of place, but it would seperate the car from the road, if you will.
Red makes it look faster too, blue is a calming color in nature, while red brings to mind passion, fire and speed in terms of emotion.
Other possible colors for the neon could be yellow, orange, or purple (black light). these are all complimentary colors to red.
As for the yellow car, well, I'd go with red or yellow, possibly green or orange, depending on your layout.
Color wheels are helpful tools that can be gotten from paint shops or art supply stores, they can help you establish a pallete to model your car from before you even start building it.
My two cents...