Branch coloring does focus on one line but I am not sure what sort of branch history it is supposed to mean. Look at this black line when only the "develop" branch is selected from the list of branches.

I recognize that I still have a lot to learn from Git. When one spend too much time trying to figure-out what those colored bars represent, you have to wonder about their usefulness. In your comment "For a arbitrary commit you can't say in which branch it was created", that is perplexing. When I perform a commit, I certainly know which branch it is done under! Those colored bars follow some kind logic that appear to be related to the lifecycle of a branch.