I looked at the Martrim linings but I think that Woolies has better colours, - but- as you note, you are very close to Martrim so it would make sense to buy from them.
I bought a roll of Oatmeal lining material based on Martrims recommendation but, having received it, I think that is too grey for the Lightstone leather interior. A guy that I know, from whom I got a quote to do the lining, showed me the Cashmere lining and I think that it is a much warmer look, and is a bit better of a match for the Lightstone.
Oatmeal may be closer, but I think that Casmere looks a bit "richer".
Adding soundproofing between the headling panel and the roof may be a very good idea and I might consider it myself. The only issue that I can see, and it has been brought up by guys in the States, is making absolutely sure that any adhesive is really high temperature stuff. Quite a number of guys have said that they have had issues later due to the very high temperatures in the American west, because the adhesive loses stickiness because the roof steel gets so hot.
It would be rare for us to see those temperatures but even if we have a good sunny, summers day the roof of the vehicle could easily be 40 degrees, if not more. I would be worried that the glue would come unstuck above the headling panel, and the insulation material would flop down inbetween the two panel, the roof and the headlining. It would be a real pain to have to take everything out again to sort it out.
Maybe the air gap is there for a reason ?
I wouldn't fancy making a big change to the roof lining colour because of the difference in colours, clashing with the existing upholstery. If it was a couple of shades different then it would probably work OK, like using either Oatmeal or Casmere in my vehicle. But I don't think that I would use silver or white, for instance, as the colour difference would be too great. But Grey or Oatmeal [which is almost Grey in the daylight] would probably work and make the interior a bit lighter.
I guess the only way is to go to Martrims place a get a look at the material in the daylight, and see what you think, but I wouldn't personally use black as I think black just makes everything dark and gloomy and makes the interior look smaller.
I looked at buying an E-class Merc or a 5 series BMW two years ago and everything was black interiors. I went to a number of main dealers looking at 2 year old [or thereabouts] models and I remember that I saw one Merc that wasn't black interir - and it was red !!
I bought a Lexus IS300h with cream leather instead.