Hi Paul,
Besides Conditional Formatting
http://www.mvps.org/dmcritchie/excel/formula.htm
This is also possible with normal cell formatting:
http://www.mvps.org/dmcritchie/excel/formula.htm#cellformat
see the table and area below it. In fact it was Myrna who helped
me learn about this. The formatting is (by default)
positive; negative; zero; text
A typical formatting for negative numbers in red is:
#,##0.00_);[Red](#,##0.00)
You might have something like
[Magenta]#,##0.00_);(#,##0.00)
the underscore is a space of the width of the next character
It is also possible to change colors with an event macro, if it is
not either of above. It is unlikely that to be used with a formula
in the cell, but you might check by right click on the sheet tab, view code.
Also check ThisWorkbook by clicking on the logo to the left of the
menu bar (view code).
http://www.mvps.org/dmcritchie/excel/event.htm