Hi Epee,
First of all, welcome to the forum!! Glad to have you here.
Yes, the density of paint applied in unit and personal marakings varied with the availabilty and type of coloring material used. Try as I might, we can't always get the profile artists (or editors) to agree to depict these machines as dirty and translucently-marked as they may have been, but I think Harry Dempsey does a marvelous job. If you'll look at the profiles in the Fokker Triplane aces book, you'll see the streaky camouflage underneath showing through the overpaint in a number of places. Sometimes paint was thined in the interest of economy, and sometimes it really was pretty densely applied.
As for the Fokker Dr.I line-up at Léchelle in late March, yes, the first aircraft in particular looks like it is very dark to a point aft of the cockpit (this has been discussed a lot). Looking at a good print I could still discern the light blue undersurface color applied as a border to the bottom edge of the fuselage in that area. This was done at the factory, so I have assumed that that area was simply very densely streaked camouflage and not overpainted, which would have obscured the blue border. Of course, I could be wrong-as some on this forum will no doubt agree! As for the other aircraft, I think they had red cowlings, struts and wheel covers only. There are plenty of Jasta 11 triplane photos which show this area from cowling to the cockpit as typical streaked fabric. The German journalist Oblt. a D. Peter Martin Lampel visited Jasta 11 in early April 1918, and he said all the triplanes had red cowlings ('Kappe', meaning hoods or cowls).
Incidentally, the Dr.I with the swastika was flown by Ltn.
Eberhardt Mohnicke. He had previously served in Kagohl 2, which used a swastika unit marking, and he brought the marking with him from that unit.
Very best regards, and again-welcome.
Greg VanWyngarden