http://www.people.fas.harvard.edu/~djmorin/chap11.pdf "Let's now start from scratch and see what the theory of Special Relativity is all about. We'll take the route that Einstein took and use two postulates as the basis of the theory. We'll start with the speed-of-light postulate: The speed of light has the same value in any inertial frame. I don't claim that this statement is obvious, or even believable. But I do claim that it's easy to understand what the statement says (even if you think it's too silly to be true). It says the following. Consider a train moving along the ground at constant velocity. Someone on the train shines a light from one point on the train to another. Let the speed of the light with respect to the train be c (~3.10^8m/s). Then the above postulate says that a person on the ground also sees the light move at speed c. This is a rather bizarre statement."
It is not bizarre, it is absurd. The person on the train sees (measures):
speed of light c ; frequency f=c/L ; wavelength L.
The person on the ground sees either:
speed of light c+v ; frequency f'=(c+v)/L ; wavelength L (Newton's emission theory);
speed of light c ; frequency f'=(c+v)/L ; wavelength L'=cL/(c+v) (special relativity).
Clearly the emission theory's prediction is physically reasonable while the special relativity's prediction that "the speed of light has the same value in any inertial frame" is a fudge - it absurdly (and implicitly in the relativistic literature) presupposes that the wavelength is measured to be L on the train but L'=cL/(c+v) on the ground.