So in the intrests of enlightening the masses, if I slot a purple Refugee (yes I do have one), will I get a purple officer in return?
Are there any special 'rules' to watch out for?
It's not a guarantee. It works exactly the same as any other assignment, meaning that a higher quality duty officer slotted will make it more likely - but not guaranteed - that you will get a better result.
The one thing I would note is that people like giving refuge to people like them, so an Orion refugee's traits will tend to be more desirable on Orion asylum assignments, and Saurians with Saurian asylum assignments. There's still a fair amount of variation in traits, though, but it's something to keep in mind when you see an asylum assignment pop up.
The rewarded duty officers will, however, always be at least green though, so even if you put in a white refugee, you'll see at least some improvement, and the rewarded duty officers will never be Civilians.