toufik7
Hi
Yes you can change it for one article as well, for this you need to create a menu with type > Articles > Single article.
Select the article in this menu.
Now go to page display tab > Add page class : http://prntscr.com/kf3ugj
Apply the css rule based on this class.
if you have any issue you can share the article page URL here and share the screenshot how you would like to change the color.
I will suggest you the changes based on the page.
Regards