How can I add a coloured, random, ragged brush stroke to a black and white graphic in Paint.net?

Question

I have a black and white photo and I want to add a sweeping brush stroke wash in colour across it so that you can see the B&W information through the colour.

A second possibility is to do a colour gradient (I hope I am using the correct terminology) diagonally, covering the whole graphic but starting in, say, a red colour and gradually changing until it is a bright yellow, for example.

Answer 1

Add a new layer, do the brush stroke or gradient, then increase transparency in layer -> layer properties