The branch name in a separate branch column would be a good start, however I would much more prefer that the branch lines in the graph column are colored per branch. You only have to add a color index somewhere in a small part of the window instead of on every entry in the list. For instance:
default = black
rel1.5 = red
rel1.6 = green
This approach would easily help out distinguishing diverges on the same branch from different named branches.