I think we always strive to give the correct solution with useful links.  And we ask that questioners always upvote good answers and when they reach 20 karma points accept the best answer to thier questions.

Now that everything is clear.  I have started to compile information about Odoo Themes.  You may find the quick and dirty theme color changes in CSS link useful.

See

See also https://www.odoo.com/forum/help-1/question/odoo-online-homepage-change-background-color-which-i-can-do-using-studio-and-now-i-want-to-change-the-menu-color-170955 for a way to do this without a module or needing to edit source code files.

Consider installing this module: https://apps.odoo.com/apps/modules/8.0/colors_customization/