I use Linux Mint - which is based on Ubuntu - and I may be able to help with the "font" issue.
Your fonts are stored in two places. Your "system" fonts are located in /usr/share/fonts and your "local" or "home" fonts are located in your Home directory in the .fonts folder.
The .fonts folder is a "hidden" directory. I suppose the easiest way to "view" the folder would be... From your Desktop, double click your Home folder, then locate the "View" tab at the top of that window. You should see the option to "Show hidden files". Once chosen you should now be able to scroll down through your "Home" folders. All the hidden, or "dot" folders, will be displayed below your "normal" folders. I hope this helps.
Why two locations? Let's imagine you have multiple users logging into you Desktop. Every user has access to the "system" fonts (but only Administrator can delete them), however the "local" or the .font folder that appears in all users "Home" folders can only be used be the one logging in. Fonts can be added and deleted at will by the user. This is useful if the user wants to add fonts that only that user wants to use.
If you are still unclear, this may also help...
http://lubuntuhowto.blogspot.com/2016/02/how-to-show-hidden-files-and-folders-on-lubuntu.htmlor this one... and scroll down to Fonts.
https://help.ubuntu.com/community/Lubuntu/SetupFor the "colors" in question two. I don't know about "config" files for QB64 but I use the "IDE Colors" in the "Options" tab at the top of QB64's window. You can either select from several "Schemes", or if you are brave enough, make your own by modifying the many "items" and saving when done. I hope this is helpful...
J