Using 18bits display on Raspberry pi with Xorg

I encounter a problem trying to use professional 18bit display (6bit by color) with a raspberry pi. Because the two missing bits are most significant bits, all display are ugly. Due to antialias, text become near to unreadable...

• G121XN01 V0 - 12.1 inch 1024x768 XGA - Operating Temperature -30 ~ 85 °C
• RT2281 LCD controller board - (Aliexpress)

You could send your suggestion to x18bit@f-hauri.ch. Solution will be reported here and to some forums, with all of references author would present.

    - setting "DefaultDepth 18" in xorg.conf doesn't work
    - setting "DefaultDepth 16" in xorg.conf work, but does worst...

Seem to be a Endianness problem...

Here are some photos of screen running on Raspberry PI, with Xorg.

Note: Due to antialias, text is very hard to read!

Last picture show the Color Level panel with texts not so readable:

   Input Levels
   [ 0   ]   [ ] Clamp input    [ 1.000 ]      [ 255 ]

   Output Levels
   [ 0   ]      [ ] Clamp output               [ 63  ] 

DefaultDepth 24

DefaultDepth 16

Zoom on Color Level panel