Partial Formatting of Cell

Hi. I am trying to find a way to make the characters before the first underscore change to a colour of my choosing (e.g. red in this case), for all cells in the first column. I presume this can be done with VBA, and I am slowly getting better at using it, but I am unsure how to do a partial colouring of the cells (I know how to do the entire cell, but that's not what I want to do). Any help would be appreciated. Thanks.

EDIT - The first cell in the attached file shows an example of what I am trying to do.