I spent some time figuring out how to make it look like Gnome top panel is included inside Unity top panel and I finally managed to reach a plausible state, so I will share my knowledge:
Install gnome-shell and gnome-panel:
sudo apt install gnome-shell
sudo apt install gnome-panel
sudo apt install wmctrl
Add this startup script:
sh -c "...
There's a native color picker for HTML5's <input> tag built into all modern browsers (some screenshots).
Enter this in browser's URL bar:
data:text/html,<input type="color" />
and click on the rendered button. Bookmark for later use. Works offline.
(Technically, this is neither a dedicated app, nor GNOME-specific; which might exactly ...
sudo apt install printer-driver-fujixerox
In Unity's Add Printer dialog, select "Network printer" then "LPD", and type the printer's IP address.
Then select the driver 'FX'.
I did not try printing the test page; but a double-sided PDF just worked!