The top of a tower of height h emits light with frequency f, speed c and wavelength L (as measured by the emitter):

f = c/L

An observer on the ground measures the frequency to be f'=f(1+gh/c^2), the speed of light to be c' and the wavelength to be L':

f' = c'/L'

Crucial questions: c'=? L'=?

Newton's emission theory of light:

c' = c(1+gh/c^2)

L' = c'/f' = L

Einstein's relativity:

c' = c(1+2gh/c^2)

L' = c'/f'

Needless to say, the answer given by Einstein's relativity is absurd so no Einsteinian would pronounce it explicitly. Occasionally Einsteinians active on the sci.physics.relativity forum offer another answer (which has nothing to do with the original 1915 theory):

c' = c

L' = c'/f'

The problem with this answer is that it is incompatible with gravitational time dilation. The answer implies that the frequency shift (measured by Pound and Rebka) is entirely due to a shift in the wavelength. Then there is no place for gravitational time dilation in this scenario - another factor (the shifted wavelength) has already done the job.

Pentcho Valev