As many might have already noticed the theming support of SharePoint 2010 was completely changed. It took me some time and a lot of research to get a good understand on how it works now. I would like to give a small summary and leave the rest to some articles which explain it quite well:
- Themes come from Office Design files
They are either created using the SharePoint web interface (but cannot be saved then) or by using Office 2007+.
Read more on which colors are applied where.
Read more on how to create theme files using PowerPoint.
Read more on how to create theme files using OpenXML.
Try out the Microsoft Theme Builder.
- CSS files and images can be themed
This means that when you create web parts for SharePoint, make sure they match the SharePoint 2010 default coloring.
Read more on how the themes are being applied and themed versions of CSS files and images are being created.
Read more on how to make your own CSS file and images to be themable.
- CSS files and images cannot be customized
There is no reliable and acceptable way to modify themed CSS files or images. Give up on trying to do so since your changes can be easily overwritten!
I hope this provides some hint on this important topic.
UPDATE: Added link to my extended theme test.
