If you're talking about doing something in Excel, I suggest you ask in an
Excel group.

If you are asking about how to colour the result of date fields in the
result of a Word mail merge, maybe you can spell out the specification? For
example, this is what you say:

Do you mean
a. I want insert dates from three Excel columns
b. For each date
    - if it's before a date I specify (how?), I want it to be displayed in
one colour
     - if it's after a date I specify, I want it to be displayed in another
colour

or what?

(if (b) is about right, you might also consider what you want if the date is
exactly the date you specify)