Varnish on top of every layer

You don't need it between coats,just a clear coat at the end to protect from possible weathering that you might be doing.

I would not use varnish- an acrylic or lacquer is handier.  Also, I would only use it for decal areas or as a final gloss coat to get a gloss finish.

Makes no sense in what you're trying to achieve by adding a coat of varnish between colors. A total waste of time really. Nathan is right though.

sherbir

So I am repainting the camo scheme on my B-52 model. I have base coated the entire model with light dust/mud brown color and now I will add two tones of green camo over this base color. I want to know which would be a better idea:
1. Cover the base coat with varnish - paint the first tone of green - varnish again - paint the second tone of green - varnish again
OR
2.Base coat - first green tone - second green tone - varnish in the end

No need for any of that. You'd have one heck of a paint layer. It will do nothing for you. Paint your camo, then gloss varnish for decals if your paint went on a bit rough, then seal the decals with a gloss or semi gloss.

2)

As long as you leave enough time for the paint to dry between colours, mask carefully & appreciate that (acrylics) can be quite delicate without a clear coat there isn't any real need to clear between colours. I've done plenty of camo birds & have only ever put a clear down as a final coat.