I like the option to color modified lines and it's even more useful with the birds-eye-view, but there are times when I'm forced to exit Slickedit, and I lose the modified line info. Would be great of this could be persisted, but I realize that's a lot of info to store somewhere and manage (determine when it can be cleared).
An alternative would be to, when opening/loading a file, diff against the base version in version control and mark modified lines accordingly. From that point on, just do the normal modified line tracking. Could even have a feature in the version control menu to update the modified line marking based on the current diff. That way, if I've changed something back to what it was before, the lines can be returned to the non-modified color.