fonts/etc_fonts/conf.avail/10-sub-pixel-vrgb.conf

<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<fontconfig>
<!--  Enable sub-pixel rendering --> 
  <match target="font">
    <edit name="rgba" mode="assign"><const>vrgb</const></edit>
  </match>
</fontconfig>