I have created a fonts.conf configuration file $HOME/.config/fontconfig/fonts.conf with the following content:

<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<fontconfig>
       <match target="font" >
              <edit mode="assign" name="rgba" >
                     <const>none</const>
              </edit>
       </match>
       <match target="font" >
              <edit mode="assign" name="hinting">
                     <bool>true</bool>
              </edit>
       </match>
       <match target="font" >
               <edit mode="assign" name="hintstyle">
               <const>hintfull</const>
               </edit>
       </match> 	
</fontconfig>


According to xrdb -q (after re-login) the following values are set:

Xft.dpi:	96
Xft.hinting:	true
Xft.hintstyle:	hintmedium

So the config seems to be ignored.