On one of the photo sites I follow someone posted this image with a leading title that suggested this was a ufo confirmation:
In 5 of the 21 frames that make up the animated gif there are 2 red, a blue, and a green dot, all in a line (you might need to pull the image into your favorite image editor and zoom in to see the second red and blue dots).
Taking pictures of things in space isn't like taking pictures in your back yard. You don't take color images, instead you take long exposure black and white images with very specific color filters over your camera lens. The images are then post processed, having each filter corresponding to a different color. These images are called false color for that reason.
This works pretty well for imaging things that don't move very quickly, but creates a very funny effect for things that are moving fast through the frame, because the object is in a different position in each color. This is what asteroids or satellites look like when they are captured in an astro photograph. The Sloan Digital Sky Survey has a whole chapter on their website on finding asteroids in their images. The pattern in the SDSS data is a little different because their imaging equipment is different than what we are seeing here. Galaxy zoo also has some really good information on funny things you see in CCD images.
Which raises a good question, what are we looking at? It turns out this is one of the sample runs of the Palomar 200 inch telescope showing off their adaptive optics in 2006. These 21 frames were taken from earth, through our atmosphere, with manipulators bending the mirrors on the telescope to reverse out atmospheric distortion. Really impressive stuff.
Update: given the rotational speed of Neptune, you are looking at between 3 and 4 hours worth of time elapse here. That means you could calculate the angular velocity. This would push for it being an asteroid instead of a satellite because it is actually moving reasonably slowly in terms of degrees per hour.
Update 2: it could also be a moon of Neptune, many of them end up about that close, and orbit fast enough that they could move like that in the frame.