Final Draft Go gives you the ability to color all of the dialogue for one or more characters. To highlight a character's lines, touch the Tools icon at the upper right...
...and then select Character Highlighting from the menu.
The script's characters will be listed. To highlight one or more characters, move the associated switch on the right to the On position:
To change a character's color either at the outset or after a color has already been assigned, touch the marker icon next to that character to display the color picker:
Touch the script to clear the Character Highlighting window away.