http://www.exploratorium.edu/hubble/tools/doppler.html
"This apparent change in the pitch (or frequency) of sound is called Doppler shift. Light from distant stars and galaxies can be shifted in much the same way. Like sound, light is a wave that can be described in terms of its frequency, the number of wave peaks that pass by each second. Just like a cosmic police car, a star zooming toward you has its light waves squeezed together. You see these light waves as having a higher frequency than normal.. Since blue is at the high-frequency end of the visible spectrum, we say the light from an approaching star is shifted toward blue, or blueshifted. Likewise, if a star is zooming away from you, any light it emits gets stretched. You see these stretched-out light waves as having a lower frequency. Since red is at the low-frequency end of the visible spectrum, we say that light from a receding star is shifted toward red, or redshifted."
If a star moving towards the observer had, like a police car, "its light waves squeezed together", then the speed of the light waves as measured in the system of the star would be, like the speed of the sound waves as measured in the system of the car, DECREASED. This is not the case, which means that, unlike the sound waves, the light waves are NOT sqeezed together (the analogy between sound and light is incorrect in this case).
Accordingly, the blueshift measured by the observer is due to the fact that the speed of the light relative to the observer is greater than c, in violation of Einstein's relativity.
Pentcho Valev