There are two places where you can alter the fonts appearance:
dconf and find
org.gnome.settings-daemon.plugins.xsettings schema. Hinting, antialiasing and RGBA order can be set there. These settings affect GTK and Unity applications.
2. Take a look at
/etc/fonts/conf.d folder. It actually contains symlinks from
/etc/fonts/conf.avail. For example, if you want to change your hinting style from slight to full, remove one symlink and add another.
sudo rm /etc/fonts/conf.d/10-hinting-slight.conf
sudo ln -s /etc/fonts/conf.avail/10-hinting-full.conf /etc/fonts/conf.d/
In your case check whether
10-no-sub-pixel.conf symlink exists in
/etc/fonts/conf.d folder. If yes, remove it and add
10-sub-pixel-rgb.conf symlink as described earlier.
These settings affect non-GTK applications like Firefox and some other.
If you need some proven resources about fonts configuration you can look at https://wiki.ubuntu.com/Fonts (mostly consists of custom
~/.fonts.conf and quite old). Another great resource is https://wiki.archlinux.org/index.php/Font_Configuration (contains multiple hints and up to date).
BTW Direct editing of
/etc/fonts/fonts.conf is not recommended. You'd better add
~/.fonts.conf with your custom settings which will prevail over the settings in