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 chevron at the bottom 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.