I am rebuilding the game engine again for more practice, this will be my 3rd attempt. After I get all the Core parts done, I am planning on revamping it to fit my needs.
One thing I did notice however was this...
After Marek got done creating the ColorOGL class to replace the structure that was in Triangle.h he built the project and started to add in ColorOGL.h into several files such as Triangle, House, Scene, and OpenGL...
For a shortcut, since we use Core.h in most places, I think it will be safe to add ColorOGL.h as an include in Core.h just like we did ErrorHandler.h
I did this myself and the code runs fine.