Could be: I give it an exterior vacuum once in a while.
Updates
– I changed the title bar colour to grey when active and black when not. When active is set to grey, the inactive colour is white by default. I had to change it to black in the registry.
– I just installed Ubuntu on Windows… 
Looks like it is a bit behind: Ubuntu 16.04.3 LTS.
PS Upgraded to the latest Ubuntu! Turns out I need to add the --proposed or --devel-release option to do-release-upgrade.