We need to make changes in SharePoint site theme and apply it on site collection and all webs under that site.
We will take two simple changes like changing the color of “Text/Background – Dark 2” and “Text/Background – Light 2” of theme “Convention”.
Enclosed in red rectangle in the figure below are the two colors which needs to be change.
First step is to download the theme “Convention”. Go to “Site Settings” -> “Galleries” -> “Themes”. Save theme on your local disk.
Open it in “PowerPoint 2010” and go to “Design” tab and click on “Colors”, following window will appear:
Click on “Create New Theme Colors..” and following screen will appear:
Change the color of “Text/Background – Dark 2” and “Text/Background – Light 2” as per need and save the theme with different name.
Upload the theme in “Themes” gallery and apply it on the site. Bad news is that it will not be applied on all the webs under the site.
For this, we wrote a PowerShell script available at this url.