I'd like to request a new feature: a SEXP to change ambient lighting (or star count) during a mission.
Right now it is already possible to set ambient lightning (level/color) in FRED. Default value is RGB=120, 120, 120, I believe. So a system with red nebulas and blue sun, would have rather red ambient lighting while the direct light is still the blue one from the sun. Now, missions which include jumping from one system to another are a problem. It is possible to change background bitmaps, suns and skyboxes, but not lighting (or star count for that matter).
It would greatly enchance visual quality if such a SEXP would be added.

Otherwise we would have to use basic white ambient light for all star systems (since otherwise jumping to a different system doesn't work).