We have a mixed exchange setup with 2003 and 2010. Ive migrated all of the shared calendars and such. We use colour categories on them frequently. But if your account is on the 2010 server, theyre all the default pale green colour. Update: I found these to be set in a GPO. Not sure why they arent showing for clients on our new server....

this links can help you http://mscerts.programming4.us/application_server/exchange%20server%202010%20%20%20upgrading%20from%20and%20coexisting%20with%20exchange%20server%202003%20(part%2012)%20-%20planning%20public%20folder%20access%20and%20migration.aspx. http://blogs.technet.com/b/exchange/archive/2008/01/10/3404629.aspx

Sorry I forgot to mark solved. I needed the GPO admin template for outlook 2010, and to add the categories for that.

Hi, Office 2010 Group Policy Administrative Template files: http://blogs.technet.com/b/office_resource_kit/archive/2010/05/03/office-2010-group-policy-administrative-template-files-adm-admx-adml-and-office-customization-tool-download-available.aspxPlease remember to click Mark as Answer on the post that helps you, and to click Unmark as Answer if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread. Thanks Gen Lin-MSFT