Assigning colours to activities and documents?

Is there any way to assign colours to activities and documents, rather than applications?

(Just to let you know, I think Slife is a great idea, and has a really nice implementation! In fact, I discovered it just after thinking that it'd be really useful to have a program that automatically tracked how I spent my time. That said, I think it would be a lot more useful if users were given greater ability to customize how data was presented, and how it is grouped.)