Change sidebar color

Hi,

I can’t find how to change the background color of the sidebar.
When I’m in an article the background color of the sidebar is : #4d0f72 and I want it to be #7d898a.

On this page it works : http://www.label-industrie.fr/category/savoir-faire/ but when you go into an article it changes and I can’t figure it out : http://www.label-industrie.fr/les-toits-paris-inscrits-au-patrimoine-lunesco/

Thank you very much for your help!

Matt