I do have a degree in Physics so here is the real scientific answer to the question of which car is the fastest. Fast cars are always blue when they are approaching you and red when they are going away from you.
Consider two objects: the light source and the "listener" (or observer). Since light waves traveling in empty space have no medium, we analyze the Doppler effect for light in terms of the motion of the source relative to the listener.
We set up our coordinate system so that the positive direction is from the listener toward the source. So if the source is moving away from the listener, its velocity v is positive, but if it is moving toward the listener, then the v is negative. The listener, in this case, is always considered to be at rest (so v is really the total relative velocity between them). The speed of light c is always considered positive.
The listener receives a frequency fL which would be different from the frequency transmitted by the source fS. This is calculated with relativistic mechanics, by applying necessary the length contraction, and obtains the relationship:
fL = sqrt [(c - v)/(c + v)] * fS
Red Shift & Blue Shift
A light source moving away from the listener (v is positive) would provide an fL that is less than fS. In the visible light spectrum, this causes a shift toward the red end of the light spectrum, so it is called a red shift. When the light source is moving toward the listener (v is negative), then fL is greater than fS. In the visible light spectrum, this causes a shift toward the high-frequency end of the light spectrum. Obviously, in the area of the electromagnetic spectrum outside of the visible light spectrum, these shifts might not actually be toward red and blue. If you're in the infrared, for example, you're ironically shifting away from red when you experience a "red shift."
Ok, got it? All fast cars are blue when they are approaching you and all fast cars are red when they are departing. They are never yellow or any other color!