Comment # 3 on bug 1188862 from Dr. Werner Fink

To do this correctly this should be done

 xrdb -cpp 'cpp -ansi -traditional-cpp' -symbols | grep -i color
 -DCLASS="TrueColor"
 -DCLASS_TrueColor=172
 -DCOLOR
 -DCLASS_TrueColor_24=172
 -DCLASS_DirectColor_24=173
 -DCLASS_TrueColor_32=174

to check supported Colo(u)r Class ... and only for the local used DISPLAY :)