Hi,
I don't know if anyone thought about it before but certainly not me.  If the building is clean (mine aren't always) and nothing needs to be hidden, I'm more attracted to the idea of ​​painting only the areas in contact with the film.  Whatever your choice is good luck and don't forget to share the result.

Massimo

If you paint the structure with Rit dye dissolved in alcohol, you will add no weight.

Finally got a picture.  The color was done with a magic marker.   The covering is SLC from the Corehouse.

Looks better in person.

I plan to paint the frame of the wing then cover it with clear film. I'm wondering if I should just paint the areas where the film will stick or should I paint the ribs and everything you can see through the open bays. Thinking about weight but would it look weird/unfinished if the ribs, inside of trailing edge ect is plain balsa?

Thanks,
Motorman

Sorry M-  I've been coloring and painting over and under clear covering for years.  Depending on the film there may be problems, so do a small test piece first.
Decals, inkjet printed logos, etc. can be put on underneath the covering.  Easy on a foam wing.  For a built up wing the decoration can be ironed onto the back of the film before applying the  covering.

Water-based paints will tend to raise the grain of balsa wood.  An enamel such as Rustoleum Gloss can go on over a seal coat on the balsa.  Various paints have a greater or lesser tendency to raise the grain.  You just have to test it.  Varathane water-based clear polyurethane should be fuel proof, but double check. Thin it with alcohol to reduce the water in it.  RustOleum has taken over the brand and might have changed the formula.  I'm only half way through a gallon of the original.

For a top notch finish, which is very presentable but not front row, you can apply the covering.  Buff it lightly with a green Scotchbrite pad an apply a coat of autobody primer- the high build variety if you can find it, otherwise a couple light coats.  Sand it all off with a block sander leaving a mottled finish.  Apply an opaque base color, usually white, to hid the mottling.  The apply your color scheme using canned enamel or spray cans of Rustoleum Gloss enamels.  It dries to a fuel proof finish, at least a week to gas off and harden up.

Applying silkspan, or the newer exam table paper(search here for it) before painting will give a nicely old-fashioned look to the final finish.