Comment # 71 on bug 904015 from Petr Gajdos

Created attachment 713959 [details]
firefox with specimen html displaying fonts black and white for smaller

Giving up!

As I said, I am able to bring up black and white fonts in gtk applications as
demonstrated with the image, I believe this is the state you want to achieve.
This is done just with:

$ cat ~/.config/fontconfig/fonts.conf
<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<fontconfig>
  <alias>
     <family>sans-serif</family>
     <prefer>
        <family>Tahoma</family>
     </prefer>
  </alias>
  <match target="font">
    <test name="font_type">
      <string>TT Instructed Font</string>
    </test>
    <test name="pixelsize" compare="less_eq">
      <double>11.0</double>
    </test>
    <edit name="antialias" mode="assign">
      <bool>false</bool>
    </edit>
  </match>
</fontconfig>
$

on top of 42.2 fontconfig settings plus, of course, instructing gtk
applications to actually use smaller sizes. The alias is there to make sure
Tahoma is preferred to stand for sans-serif. I can not tell anything about kde
applications, though.