Hiding filler that shows through

This problem sometimes occurs when filled areas are not primed before painting. It is always best to prime filler and/or apply an extra patch of paint to filled areas. This is especially the case for water-based paints

Tools and materials
Paintbrush, primer, roller, paint

This problem can occur with some types of filler.
Recoat the patch of filler with a suitable primer, or if you are painting with emulsion, prime with full-strength emulsion.
Recoat the entire wall.