Thanks.
The Jasta 18 bird has had its tail painted pure white, then the ribs have been masked:

Then a coat of off-white oversprayed with white to melt all up. It's not much visible on photos, it requires to be discrete but it works. On Udet's machine, the tail has first been painted white, the stripes have been masked and a coat of black has been sprayed. After that, the cockpit padding received a basic brown color.

The wings uppersides have been painted light tan to alter the lozenge color in an attempt to simulate the linen color underneath:

The lower sides are white in order not to alter the lozenge colors and have white areas under the crosses which were printed along the lozenges. All holes for masts, wire hooks and cables have been drilled, then the radiators have been painted.
I started applying the lozenges on Udet's upperwing, but the ink started to flake when I rubbed it with a cloth...So, to prevent this, I had to spray another coat of varnish on all the decals I had printed, and re-print this area.

This shot shows how the undercoat alters the lozenge colors:

Udet's both lower wings. I still have to paint the tape that goes around the whole wing, since I couldn't print this with the rest.
Printing the rib tapes with the lozenges helps sparing a lot of time.

I was eager to see how would look the Jasta 18 upperwing with the red decal including rib shading and crosses. There will be some touch-ups to do with red paint but it works and I like the color. This wing upperside was painted white as an undercoat not to alter the shade of red and to create white areas around the crosses.

Now I need to make a mix from red paint to get the same shade and do the touch-ups, and paint the front fuselage the same color.