a photon does not have an amplitude, an amplitude for a photon is not defined (unless you mean the probability amplitude). The red and blue photon differ by their wavelength. For example a red photon [itex] \lambda = 800 [/itex]nm and blue photon [itex] \lambda = 400 [/itex]nm.
When you talk about amplitudes you usually refer to electromagnetic waves amplitudes. But one single photon does not have an amplitude.
A single photon does have an amplitude.
The amplitude of the vector potential in an electromagnetic wave is
given by Nh\nu, where N is the number of photons in the wave.
Amplitude does not relate to color, which depends only on frequency (or wavelength).