You might have been using Diodon for a while and are wondering why there is no monochrome icon in your panel but instead a colored fish?
This could look like the following:
The icon does look a bit out of place in this specific theme. Unfortunately it is impossible to create an icon which suits every theme very well and if we would use a monochrome icon as the default it might not even show up on certain themes. That’s why we have decided to have a colored fish as the default panel icon as it is at least visible on all themes. For some commonly used themes we made some exceptions to use the monochrome icons directly.
However, in case you use a completely different theme and you would still like to have a Diodon monochrome icon there is a fairly quick way to do it.
You can use following command if you have a dark theme:
sudo ln -sf /usr/share/icons/ubuntu-mono-dark/status/22/diodon-panel.svg /usr/share/icons/[MYTHEME]/status/22/diodon-panel.svg
or this command with a light theme:
sudo ln -sf /usr/share/icons/ubuntu-mono-light/status/22/diodon-panel.svg /usr/share/icons/[MYTHEME]/status/22/diodon-panel.svg
In both cases replace [MYTHEME] with whatever theme you are using.
And last you need to update the cache of your theme with the following:
sudo gtk-update-icon-cache /usr/share/icons/[MYTHEME]/
Done. When you now close Diodon and open it up again a monochrome should be shown in your panel.
What I would recommend you though if you want to have a more permanent solution: Get in touch with your theme author and ask whether he would be willing to ship a monochrome icon for Diodon. In the end does the author know best what suits its theme and when the Diodon icons are shipped with the theme itself all users will benefit.