I think it would be beneficial to allow users to set colors for specific commenting tools or tools in general (strike through, text box, line, rectangle etc.) based off a selected profile. I am constantly switching specific tools between blue green or red based on the task, document, or customer i am working with. Allowing a quick change profile selection ( can also include signatures etc.) would allow people to have a real customizable system. If you are working contract for multiple companies doing side jobs this can let you keep track of each profile and their requirements for colors or images on signatures etc. very easily.