You really should prime the walls after you patch - that will eliminate the "flashing" spot where you may not have sanded.

I would not add food coloring - when the patch dries the coloring would be re-activated by the paint you applied next - and bleed through.

One thing you could try is a very light pencil mark near where your patches are - that way you would be able to see the general area - and they will sand off.

You also could try a halogen work light shining up the wall - painters do this all the time to check for missed spots - any areas you have patched will shine like a beacon.

Mr. Paint

Interesting idea, but I use a pencil to circle the spot lightly. You are going to sand and re-paint, anyway, so why worry about it or make it more complicated?

Thank you both for your replies. I think after reading your replies and replies on other boards that I'll pass up the idea of the coloring, and just really work hard with the lighting. Pencil marks too, though with the amount of damage on the walls (prior owner taking off wallpaper - spider marks all over) that the wall would look like a crossword puzzle.

Thanks again,
Cathy

easy get a sanding pole and sand the whole wall (a 5 minute job) prime then paint,now you will have a new nice looking wall withour worrying about it.