So as of a couple minutes ago, New Horizons just passed by Ultima Thule, the closest it's come to an object since about 30 minutes after liftoff. It will phone home in a few hours, live stream stuff resumes around 7am PST.
Latest coming into better focus. It won't be until February until we have the highest resolution images that were taken. A lot of science will be coming down for a long time. Here's the latest image (edit: actually, might just be a better processed first image).
Anyways, the big thing so far today is they were able to confirm the probe survived the encounter. The trickle of low res images begins soon.
They're either going to be red, blue, or green I guess. Based on how our eyes work. Our sun is greenish yellow, right? It may be no more complex than color theory and an indication that there was more heavy red stuff in the protoplanetary disc than blue or green. A lot of words to say it's red because it's red. Not very satisfying. Maybe there's a better reason.
Most of the not-star solar system is red though. Just Jupiter being mostly red makes that true. So really it might just be initial conditions. Might just be that simple. Probably also something fundamental about how light works. Earth is pretty red underneath the water and biomass.