I'm using Ubuntu 20.04 Desktop, and I'm still using apps that do not work in gnome (my VPN for example.)

I've installed Unity 7.5 as my window manager, and everything works, but the theme is not my favorite I switched it in settings->appearance->theme to high contrast, and now I'm stuck with that - there are only two options in the drop-down and both are high contrast it seems.

Desktop pic

After selecting adwaita, I think I'm in high contrast mode because my settings panel looks like this:

enter image description here

How can I add a theme?

I followed numerous tutorials that say, install unity-tweak-tool

sudo apt install unity-tweak-tool

It installs but does not run, instead, I see:

$ unity-tweak-tool
Error: schema com.canonical.Unity.ApplicationsLens not installed

It also shows an error in the GUI, but does not launch. I think every tutorial I found to add a theme requires the tweak tool.

  • Adwaita is the default theme's name, it shouldn't be high contrast.
    – gronostaj
    Nov 23, 2020 at 15:46
  • I added the screenshot of my settings panel, I think you are right? I'm not exactly in high-contrast, as some icons are colored? But I'm not sure.
    – nycynik
    Nov 23, 2020 at 16:02

2 Answers 2


A subset of nycnik's answer got it working for me:

sudo apt install unity-lens-applications
sudo apt install unity-lens-files

The answer to installing lens apps is here

Partway down, it shows how to install the tweak tool:

sudo apt install unity-lens-applications
sudo apt install unity-lens-music
sudo apt install unity-lens-video
sudo apt install unity-lens-files
sudo apt install unity-lens-photos

After running those (I suspect it was actually the first one in the list), unity-tweak-tool will run as expected, and you can choose a new theme.

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