I have installed the Arc-Dark theme and paper icon theme to customize my Ubuntu 17.10 experience. The theme though doesn't change my sign in screen color scheme from the purple/orange to anything, and it doesn't change the window snap color from orange. As far as I can tell these are the only things it doesn't change though. I have dconf installed but I can't find anything obvious to edit to change these orange colors.
So this question is a month old but it is unanswered and I found how to do it in Ubuntu 17.10
There is a css file in
Open it in your favorite editor, with
sudo gedit /usr/share/gnome-shell/theme/ubuntu.css
scroll down to the following lines:
/* Tiled window previews */ background-color: rgba(0, 0, 70, 0.5); border: 1px solid #000000; }
(For me they were around line number 646)
You can change the
border properties to a color of your liking.
As you can see mine are set to dark blue and black.
The following link is a great tool to find a nice color: https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Colors/Color_picker_tool
After you are done, save the file and log out and back in again for the changes to take effect.