Properly mixing color Options

[Astroboy]

Hey gang, I finally discovered an easy way to align images of various celestial targets taken at slightly different times! I used a plugin for ImageJ called bUnwarpJ. I'm really pleased with most of the results I've gotten so far. I've noticed that the receding limb sometimes doesn't warp as well as the approaching limb, though. That's something I still need to figure out, along with mosaicking and the issue I'm about to bring up.

Anyway, to celebrate performing this pretty rudimentary image processing task for the first time, I tried aligning Dawn images taken through filters 2, 7 and 8 (corresponding roughly to green, red and blue) using .img files I had converted to .gif through NasaView. The thing is, my resulting color images keep coming out looking incredibly garish. One attempt ended up with a bright pink Ceres.

I've noticed a lot of raw NASA images, calibrated or uncalibrated, vary incredibly wildly with respect to brightness, and even across images taken through the same filter with the same exposure. How am I supposed to rectify this, or even begin to know what to do? This has been driving me crazy for a while. I know there's no such thing as "true" color, that color is subjective, etc., but I've always assumed that a given combination of three frames taken through three different filters can be mixed in a specific way that is scientifically useful, predictable, and proper or something.

I guess what I'm asking is, how do you guys decide on how much of each filter to use when mixing color?