I've been thinking about this for a while now. I like that the Colonist heritage is there in game to represent those whose background is from one of the off world stations or colonies, but I never really gave it much thought as to what it really means, as far as appearance. Any other nationality, we have real life examples of to use a base as far as describing what a character with that background might look like, but since there are no off world residents just yet, we have no baselines for colonists. So, what follows is the conclusion that I have drawn, though I'd be interested to hear others opinions.
Most space travel and development seems to happen it the richer, first world countries, namely the US, Western Europe, Japan, and of course Russia, though that is an exception to the rich rule. So, the majority of the early, and even possibly later, offworlders would be either white or Asian, with a smattering of other ethnicities thrown in.
Presumably, even with advances in technology in the field of space travel, there still isn't a ton of cross over between offworlders and terrestrial inhabitants. And, as space colonization has been happening in the Sindome universe for at least a couple generations now, there has been enough time for the above mentioned ethnicities to start to merge into something new and distinctly offworlder. In short, colonists would tend to have a mixed white/Asian look about them.
Additionally, living or even spending part of ones time in a low/no gravity environment has already been shown to lower both muscle mass and bone growth, so we can assume that most offworlders would tend toward the thinner side, while the lack of gravity compression the body constantly against the ground to generally allow them to grow taller.
So, colonist equals mixed heritage, dominated by Caucasian and Asian influences tending to be tall and thin. Skin would still generally be lighter, but eye and hair color would tend to be darker. However, there will always be exceptions, since you could always have a colonist with a strong African or Latin American background, giving them features that match more with said background, while still showing influences of the dominate white and Asian heritages. Okay, I think I'm done for now.