The file tabs are annotated with a dot or cross to show if the file has been edited. I find I have to read the tabs to find dirty files rather than just seeing then automatically.
I don't think the correspondence of dot and cross to edited and un- edited is obvious or natural and it would be better to no show any annotation for un-edited files. Colouring the name of edited files would also make it much easier to see at-a-glance if something was dirty.
Dave.