Painting light over dark red

I think what I would do here is an undercoat of brilliant white matt emulsion paint, which is cheap, has excellent coverage and filling properties, dries quickly, and leaves an excellent surface for just about any other paint. It will also be obvious if you haven't covered the old paint well enough. I wouldn't use any undercoat which is darker than your top coat.

I would wash the existing walls with sugarsoap before you start.

Had a similar problem a few years ago with a brown - yes, brown! - wall. Two coates of good quality white emulsion, followed by your colour (perhaps more than one coat, see what it looks like when dry).

Good luck

Barb

I have just repainted a room that was very strong yellow and is now very pale cream. I put one coat of white silk emulsion on first then followed by two coats of pale cream emulsion. The only way to be sure is to try it on a small test area first to see if the final colour is the intended one.