While doing some research on the "pan de mur" of your question, I came across this site:
http://www.essentialvermeer.com/proust/proust.html#.XRPTButK... . The article discusses a "petit pan de mur jaune" mentioned by Proust in the "La prisonnière" volume of his Recherche. The article translates "petit pan de mur jaune" as "little patch of yellow wall", which does not really fit your context and is, therefore, not useful in this case. However, I did read the entire article and found it fascinating. It is worth the time, at least if one is not occupied with project work.