As Paul has so kindly pointed out Jerry the screen on my Sea King is a flat green. If you look (entry #57) initially as suggested by the instructions it was to be blue, but this was yuk. So I found a sliver of green plastic film in the junk box, can't for the life of me remember where it came from but any form of thin green plastic that is partly transparent will do. This I cut to shape, did a test fit and then removed that yucky blue and repainted it a light grey, using an enamel paint. Let the paint dry a little and then position the film, pressing in and hopefully the wet paint will act as a glue sealing the film down. If when dry it is not looking secure then use a dab of the white wood glue round the edge. Once the wood glue is cured, you won't know it's there.
Hope this helps and BTW, had I not got the green film I would have used the plastic from a coloured transparent folder sleeve found in any good stationers.