This is a fairly standard Special Relativity problem.

Not to grok all the maths here, what you need to account for is the individual photons coming from different points of the ship, travelling exactly at the speed of light towards the observer. Extra care for the moment the photon jumps the Alcubierre drive bubble frontier.

Since wavelenght (or frequency) is affected by relative speed of the emitter and the observer, we should start thinking that a standard Doppler Effect belongs here, with reddish light for a receding spaceship and blueish for an approximating one, but that is not true. A ship in an Alcubierre drive bubble is not moving, the bubble itself is, so there is no wavelenght change.

What is interesting is how the photons traverse the bubble. I think on that as a very extreme refraction, not caused by any material but by the metric of space-time being compressed or expanded.

Two effects there: one is that of photons coming from different distances (the standard effect that causes you to see both a complete side of a cube perpendicilar to you and its front at the same side) and another caused by refraction, in which light is simply changed of direction.

A resume could be that you see a very very distorted image, in true color.

This is a fairly standard Special Relativity problem.

Not to grok all the maths here, what you need to account for is the individual photons coming from different points of the ship, travelling exactly at the speed of light towards the observer. Extra care for the moment the photon jumps the Alcubierre drive bubble frontier.

Since wavelength (or frequency) is affected by relative speed of the emitter and the observer, we should start thinking that a standard Doppler Effect belongs here, with reddish light for a receding spaceship and blueish for an approximating one, but that is not true. A ship in an Alcubierre drive bubble is not moving, the bubble itself is, so there is no wavelength change.

What is interesting is how the photons traverse the bubble. I think of that as a very extreme refraction, not caused by any material but by the metric of space-time being compressed or expanded.

Two effects there: one is that of photons coming from different distances (the standard effect that causes you to see both a complete side of a cube perpendicular to you and its front at the same side) and another caused by refraction, in which the photons' direction is being changed.

A summary would be that you see a very very distorted image, in true color.