http://www.mvps.org/dmcritchie/excel/condfmt.htm

Found the answer --> you need a helper column, unfortunately...

2 ways of doing this.
1)  Use a 'cheat' column and conditional formatting.
 Advantage:  If the data changes, the formatting changes.
 Disadvantage:  Having an extra column with a formula
2)  Use a macro.
 Advantage:  No extra columns or formulas to maintain.
 Disadvantage:  If the data changes, the formatting doesn't change unless
the macro is re-run.

Using option 1...
- Insert a blank column in Column A
- In Cell A1, put the number 1
- in Cell A2, put the formula...
 =IF(C2=C1,A1,A1*-1)
 It is comparing Apples to Pears to Bananas to Monkeys to find out when the
data changes.  The value in column A will change from 1 to -1 everytime the
data switches from apples to pears, etc.
- Copy the formula in A2 down to the bottom of the data.
- Create the conditional formatting...
 - highlight the entire worksheet
 - Format>Conditional Formatting...
 - Condition 1:  Formula is
                 =$A1:$A1=1
 - Format>Patterns>Green
- All rows that have a '1' in Column A will now turn green.

HTH,