What I do for darkvoid is generate random number of point stars, a few larger sprited stars all on a sphere, I distort the colour towards blue or red randomly too. Then I generate a few layers of 3D noise of various colours and merge the whole lot together. By priming the random number generator with a seed when I start the process I can guarantee that for the same seed I will get the same background. So I could use say, the sector names hash code to seed the rng.
Some backgrounds have no nebula type things, just stars, some have faint nebula, so are a mass of bright ones, it's quite fun sometimes to just sit there generating new backgrounds to see what falls out
If you run the darkvoid demo from the website
you'll be able to see the background for the 'first' sector.