For dark Qt themes, it is hard to read the pixel color information on the bottom left, like the coordinates or RGB values. This PR proposes a way on how the dynamically sets the font colors based on the system's theme.
Original Example:

With patch:

For Windows, nothing is changed (tested on a windows 11 system), because the font color is #000000 when using the default Qt theme.

Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

• I agree to contribute to the project under Apache 2 License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
• The PR is proposed to the proper branch
• There is a reference to the original bug report and related work
• There is accuracy test, performance test and test data in opencv_extra repository, if applicable
  Patch to opencv_extra has the same branch name.
• The feature is well documented and sample code can be built with the project CMake