Here's a quick and clear question: How to paint,(with which color and so on..) 1:35 scale periscope armor lenses.

Thanx! John.

Not as clear as you think.
You could go the KISS route and go semi gloss black. Give's them a bit of shine.
I've seen guys who will glue a piece of 35mm film over in as glass. This gives a glass look in almost a flat color.
The period may have an affect on the color used. I know the new Tamiya Sgt York Anit Aircraft system said - blue.

If I were building it and couldn't find specifics I'd go semi gloss black.

Try to have a look at this previous post:

https://armorama.kitmaker.net/forums/9085&page=1

Some people paint them gloss black or silver and then lay a clear coat on it to give it a sheen.

This is how I do it:

I use Tamiya's Clear paints for this to achieve a depth that simulates the thick glass of the real. First I paint the area medium grey (acrylic). When that is completely dry (24h), Clear Blue and Clear Yellow is mixed to create a greenish tint that is applied to the surface. The clear paint allows surface underneath to show through, and also dries glossy. Different shades of green are possible and even encouraged for a realistic effect.