Colourist who are they? what do they do?

I have done some personal research on colourist from the previous lessons to try and deepen my knowledge of this "colourist" role, I now know that they are artist who use colours in a skiful way to contribute to a scene, the colourist is involved in colour grading in which takes place in the post production stage of filming, the use of colour grading is to set the crrect lighing in a scene and help contribute to a special effect in order to make it look as realistic as possible.
It is become even more harder for colourist  because of 2D and 2D films making the palettes more difficult