Hi Matt,
read about:
Conditional Formatting
http://www.mvps.org/dmcritchie/excel/condfmt.htm
Select the cells you want to be colored
base the formula on the active cell
in this case the columns are absolute so as long as the
active cell is anytwhere on row 1 the formulas will work,
they are checking Column D.
format, conditional formatting
Duplicate identifications (yellowish first among duplicates, greenish for actual duplicates)
formula 1 is: =IF(COUNTIF($D:$D,$D1)>1,COUNTIF($D$1:$D1,$D1)=1)
formula 2 is: =IF(COUNTIF($D:$D,$D1)>1,COUNTIF($D$1:$D1,$D1)>1)