I think I've figured out what the problem is.
The ambient lighting seems to have an effect on how things like text, orbit lines and the HUDs look.
When I first started playing I thought the lighting had been improved.
Everything looked pretty and all the lines were smooth and the text was, erm, legible.
Then, as I travelled around, I realised the cockpit HUDs looked awful.
The problem is, if I go to a system where there's a red giant, producing a lot of red light, the orbit lines, text and HUDs also become very red.
They look massively oversaturated and blurred to the point where most of the text is just a bright red "blob".
So, I increase the gamma setting and reduce the HUD intensity and it all looks nice again.
Then, if I go to a system where there's a bright yellow or white star, the orbit lines, text and HUDs become very white.
They look massively washed-out, colourless and (again) blurred to the point where they're unreadable. Again.
So, I dial back the gamma and increase the HUD intensity to restore some contrast and colour again.
And then I end up back in a system with a red star again....
A lot of people seem to think the new lighting works well so I guess it's something that I'm just going to have to get used to, unless FDev can implement an option to disable the new lighting.