An Alcubierre drive essentially creates a black hole like compression of space-time ahead of the ship, a white hole like expansion behind it, and a time space neutral area in a ring around it. So depending on the angle light hits it will make different things happen.
The area behind the ship will exert an outward curve on all light that approaches it but does not necessarily contain energy to emit; so, it may not be all that bright. At low speeds a negative mass would look like a white translucent plastic blob, but as the field intensifies, it will act more opaque and create a less scattered reflection making it more mirror like. In the case of FTL, moving faster than light means that no light can catch up from behind to reflect off of it and light it overtakes will not be able to be pushed away faster than it's being hit. This means light will radiate out like a cone from the rear field following a similar pattern to a sonic boom.
Light can move through the ring of normal space around your ship but it will all get swept up in your white-hole field meaning you will not be able to see the shape of your ship at all.
The positive mass in front of your ship will absorb all light; so, nothing to see there.
All these factors combined mean that you will only appear as the flat disc of light emanating from your rear negative mass field.
However, light emitted when you are closer to the target as you approached it will show up first followed by what was emitted earlier. This means you will see the "luminescent-boom" in reverse. You may also see the ring of light appear to be imploding faster than light if you are traveling between 1c and 2c. This is just an optical illusion caused by the light all catching up to you at about the same time. The faster you move, the slower the ring will appear to implode and the dimmer the light will be.
Last question is color. Despite many answers saying there will be no redshift, this is simply is not true. Red shift is caused because waves of light emanate in areas of space that are changing over time relative to your position. How that change happens is irrelevant since all light leaving your warp bubble will be moving at 1c. As a ship accelerates towards you approaching the speed of light, you will see it blue shift. As it hits 1c all light waves will be momentarily compacted into a super dense gamma ray burst, but what is cool is that once the warp ship exceeds 1c, it will actually red-shift even while moving towards the observer because the waves will be inverted and you and will only see a blue shift at certain angles where the relative angle of the ship to the observer creates a relative approach velocity between 0c and 1c
One last detail to be aware of is that by the time you begin to see this light implosion the ship has already either reached you or passed you; so, there is one additional phenomenon that is worth note: What does an FTL ship look like coming out of warp right next to you?
Remember the black hole in front of your ship? All of the light and matter it sucked up while in transit will be released when you come out of warp. Let's assume it takes time to slow down a warp ship as you lower your warp field. This means that moments before the ship arrives you will see a very blue shifted orb of light appear out of nowhere as the black hole stops being strong enough to hold all of its light. It will appear to be moving faster than the speed of light, but that is an illusion, once you see this, it means the ship is moving at less than 1c. You will also see a light ring start to expand out from it. This is the light ring I discussed before as it appears at less than 1c. As the ship slows down the blue shift will begin to fall off, and the light ring will begin to reverse direction and redshift as the inverted wave phenomenon begins to catch up to you as previously discussed. When the ship arrives, you will continue to see the still the imploding light ring fading off into the distance behind it.
