Het Officiële W.J. Maryson Forum

I know that I'm Dutch, but my script 'Tears for Christmas' is in English and well the following message I copied from my own post on a different forum:

In my script I have to give my FMC Samantha a flashback, the flashback occurs when she sits on a window sill and looking at the rain falling outside. Her brother and MMC are talking about someone else so they don't notice Samantha.
How do I bring in the Flashback?
How can I let the reader know that a Flashback is next? I mean I can let the sounds of the two men talking go softer, but then? Do I have to make another slugline?

Does anyone of you have any knowledge on script writing, screenplay scriptwriting that is.

It depends for what audience you're writing this screenplay. If it's for theater purposes rimple/blur is a bit difficult. A very common theater technique is fading the light on that part of the stage, while lighting another part where the actors for the flashback are standing. Meanwhile the FMC should continue talking and at some point the flashback Samantha could take over.
If it's for film purposes you have a whole window of opportunities. Going from color to black and white/sepia, having the fmc start the flashback with a "voice as thought" which is taken over by the flashback or the rimple/blur technique.