Change color in rtf memo control

[learningonthefly]

I want to have multiple users editing data in one form. Each user will be
assigned a color. Anytime they edit a field the color of whatever they type
will change to their assigned color. These fields are all in the new rich
text format memo.

So, basically the control will already contain text in black, but when a
particular user starts to edit the field, anything they type appears in a
separate color. That way, in the end it will be easy to see what changes each
user made. I know how to assign the colors but I don't know how to change
what they type to a new color (while leaving the rest of the text in the
original black)

Any thoughts on how to approach this. I can't find much info on working with
the rtf memo field in terms of making changes at run-time.

Thanks