Your comments

This would be useless for non-trivial repositories. One of ours is a quite clean one, but we have 4 branches developed in parallel. All get merged back and forth to the master. Hence, every commit of some older commits would show the same branches.

This won't work. The blue line also is part of v4.93.xx. Also, we only take colors from a quite limited pool, but there can be dozens of branches.

In this simple example this might work, but for others it might fail. I line or a commit does NOT belong to a branch in Git. A Git branch is nothing else than a named pointer to a certain commit.

Imagine you move the mouse over the blue line of the 3rd row from the bottom. It belongs to branch (origin/)v4.93.xx and (origin/)creatique_1132.

This requires a Git server configuration. Nothing that can and should be done by a Git client.

Yes, the line

graph.merge.text=#808080

should cause the effect.

You may change the colors according to your needs in the preferences.

Where you would expect to see this feature - in the Log (having stash files selected) or should the Apply Stash command should list all files for the index, working copy and untracked files)?