Before I paint the interior of my house, I would like to see a preview
of wall colours first.

I have the photos of my interior and have scanned in my paint colour
swatch.

I have also managed to select the walls in question so I guess all I
need to do now is create some kind of mask and colour burn? I just
can't seem to work it out!

I want to quickly be able to quickly pick a colour from the scanned in
colour chart and my walls magically change colour (taking into account
the shadows/bumps in the wall etc).

Thanks