Rather than painting the anti-laser filter colours on modern AFV periscope lenses, I have found a very simple and effective alternative. Using illustrations in a glossy magazine, apply a piece of sellotape over areas of purple, deep red and orange (and other appropriate colours), and cut out tiny strips (just big enough to cover the individual periscopes ... about 1mm x 2mm on a typical 1/72-scale tank). With the end of a cocktail stick, apply a thin layer of PVA glue to the face of the periscope, and lay the lens over this.
With careful choice of colours, and the sellotape providing a realistic reflective quality, the result is quite satisfactory for this scale.

so on this side of the pond is it called scotch tape ?

John,

Exactly so ... I've just used this method to replicate the filter coating on my 1/72-scale Stryker periscopes, and I'm really pleased with the result. Of course, it's important to select colours that are not too bright. All too often I've seen the lenses replicated using colours that are rather garish. In real life, they are quite subdued (unless the light is directly on them).
The layer of sellotape (or as you call it 'scotch tape') creates a very subtle refraction of light across the surface when you view the model from different angles.

Thanks for the reply

I usually go to local dollor stores and buy inexpensive bags of what they call "bangles". it's a form of mylar glitter that's cut into various shapes that I use for the lenses. I bought a bag for less than a dollar and I'll never use it all... In the U.S. we have a store called 'Dollar-Tree"... That's where i bought mine. I was in the 'Party' section.

HTH

MatthewC