conf.d/10-sub-pixel-vbgr.conf

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