While you should have the area in question checked, it is also possible that the problem could be ghosting. What is ghosting? Ghosting occurs when tiny air particles stick to one specific area in the interior of the home. Many times, this could be due to poor air flow or poorly distributed insulation, consider some examples.
Maybe you notice in your kitchen certain parts of the wall behind the stove have a yellow tinge, this could be due to insufficient venting in the overhead fan or hood. Possibly you have baseboard heaters and there is grey or black discoloration above the heaters, this is due to the hot air drawing in the cool air just above the floor and the tiny particles in the air then stick to the wall. Another scenario could be just around the fireplace, soot stains could form on the walls just outside of the fire box.
This may help you to take into account the air flow and insulation of your home and understand some reasons there could be discoloration on certain areas of your home.