In Excel 2007 think-cell charts not updated when you change the background color or a formatting.
If you are using conditional formatting to change the background please refer to the knowledge base article KB0174.
This problem is caused by a bug in Microsoft Office Excel 2007 that is fixed in the latest version of Excel 2007. Please install SP2 or SP3 for Microsoft Office 2007 or hotfix KB954947. The installation of the hotfix requires changes to registry as described on the website.