I was also trying to change the color palette due to I am unable to code with the default... that soft colors are so difficult to see...

I realised the problem is that, by default, files are opened with a new text editor "C/C++ Editor (LSP)" which I think is not configurable...

Solution: Right ...

Project
Properties
-> C/C++ General
Indexer: Configure Workspace Settings ...

Index source and header files opened in editor

THANKS