System Color file
In config.pro add a line:
system_colors_file
Give it the value X:\<directory>\default.scl
Where X:\<directory> is the place you want to put a default color file.
The default.scl can have any name with the extension .scl.
Now create a text file with the following in it:
SYSTEM_BACKGROUND_COLOR 0.000000 0.000000 31.764706
BLENDED_BACKGROUND no
SYSTEM_TOP_BLENDING_COLOR 0.000000 36.470588 60.784314
SYSTEM_BOTTOM_BLENDING_COLOR 0.000000 6.666667 19.607843
Name it default.scl or the name you chose.