In byobu (with tmux as backend) I accidentally pressed the Ctrl + Shift + F12, activating the Mondrian squares easter egg. I did close all splits opened by that "feature", but from then on, all existing windows and splits in byobu are not displayed correctly.

There's a white line between all splits, and the current input focus is no longer visible. (i.e., when I press Shift + Arrowkey, nothing visibly changes, where there used to be an orange line next to the active split).

I looked through files in my ~/.byobu directory, but none of the recently changed files contained anything that looks related.

I'm running byobu version 5.106, tmux 2.1, Ubuntu 16.04.

This is a headless server, and I access it via cygwin/ssh, but it's the same if I ssh into it from an Ubuntu machine.

Screenshot of the issue

3 Answers 3


You could repeatedly hit Ctrl+F6 to kill the active split until all squares are closed.

  • This closes the easter egg, but unfortunately it does not undo all the settings changes made until you have closed all current panes in all sessions and restarted byobu/tmux. Apr 27, 2019 at 23:15

It's a long-standing bug. Please set it there if also affects you.

I accidentally notice that setting (new or unchanged) escape sequence on Launch byobu-config window (F9) fix the issue.

You can remove that useless keybinding from /usr/share/byobu/keybindings/f-keys.tmux (not sure yet for just one user):

# Remove system-wide C-S-F12 keybinding
sudo sed -i 's/^.*mondrian/#&/' /usr/share/byobu/keybindings/f-keys.tmux

NOTE: if you have tmux from v1.9 or newer, note that you will need to translate the styling commands below as documented at: https://github.com/tmux/tmux/wiki/FAQ#how-do-i-translate--fg--bg-and--attr-options-into--style-options

You can undo everything that the easter egg changes by closing all tmux/byobu sessions completely. When you next start one it will have your usual settings because the changes made by the egg are not saved to any of your config files. If any sessions remain for this user then all new sessions get the changed settings.

This doesn't help you if you have any active sessions that you don't want to close right now, which is probably the case. You can unpick the settings with individual commands, returning them all to Ubuntu's default, but I'm not dived in far enough to quite do that yet. Setting the border colours to something more useful (which might be all there is to change back, I've not noticed other issues yet) is easy enough though, you can do so by running the following commands:

set -g pane-border-bg colour235
set -g pane-border-fg colour239
set -g pane-active-border-bg colour18
set -g pane-active-border-fg colour239

This example sets the borders to grey colours, except the active border which becomes deep blue.

Each command is run by using your command short-cut then : then the command then enter, for instance if your shortcut is the Ubuntu default:
F12:set -g pane-border-bg colour235enter
F12:set -g pane-border-fg colour239enter
F12:set -g pane-active-border-bg colour18enter
F12:set -g pane-active-border-fg colour239enter

Note that the international (English English) spelling of colour is deliberate. If you have a recent version then you can use the American English color instead, but this was not always the case so may be best avoided for compatibility.

For a list of the standard colours, see the image below. You can also use HTML-style six-hex colour codes if you want finer control (again this does not work for older releases, but you are unlikely to have a release that old) like so: F12:set -g pane-border-bg "#ffdd00"enter.

tmux standard colour palette

  • The above tmux style syntax seems to have changed in mid 2019 [github.com/tmux/tmux/issues/1689]. If I figure out the new syntax I'll fix this answer because it sounds like the solution I'm also looking for
    – pufferfish
    Mar 9, 2023 at 15:47
  • @pufferfish - there is a FAQ answer for this issue at github.com/tmux/tmux/wiki/… - I've added a reference to the question. No time to more properly update the question and test what I've written ATM, feel free to beat me to it if you have a moment! Mar 10, 2023 at 15:56

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