Can it be applied over Latex wall paint, and what color will blue be if applied to brown walls? Do the walls need to be blue?

Clearneon works great on latex wall paint. It works best on semi-gloss, egg shell surfaces. Usually the color of the wall paint will not effect the color of the Clearneon paint. If you put Blue Clearneon on a black wall and it will look the same as if it was on a pink wall.