I think it is
in the [Appearance] section of "qcad.ini".
Set this value to for example:
Anyway a good idea, because the default is too dark on black background to see on a drak screen anyway.
I also changed GridColor and MetaGridColor to a value that give me more contrast on my common Trinitron Sony monitor. (Developers like to work in the darkness, so they have to tune down there monitors to a minimum of brightness. But this is not the commonly used setup on most working places.)
The "Selecting box" color used by the mouse pointer: I did not find out if it is possible to change that color.
If you have a setup of qcad.ini etc. done for different color blindness, please let us know so that we can publish it on our new planned Support page.
So please try different values of colors, etc. and post the whole "qcad.ini" file here. Provide also the type of your monitor (common Trinitron, or TTF Flat screen, LCD Notebook, Plasma or whatever.)
And your graphic gard or other special settings you use on your operating system like Windows color scheme for spectial setups.
Sometimes it is also possible to setup different color temperature directly on your monitor hardware of your Trinitron Monitor or whatever type you have to give you a better view as needed in different environments.