When a Git process is running for side-effects, Magit displays an
indicator in the mode line, using the magit-mode-line-process face.
If the Git process exits successfully, the process indicator is removed from the mode line immediately.
In the case of a Git error, the process indicator is not removed, but
is instead highlighted with the magit-mode-line-process-error face,
and the error details from the process buffer are provided as a
tooltip for mouse users. This error indicator persists in the mode
line until the next magit buffer refresh.
If you do not wish process errors to be indicated in the mode line,
customize the magit-process-display-mode-line-error user option.
Process errors are additionally indicated at the top of the status buffer.