conditional fomatting

[mas550]

i am looking for an easy way to alternate the colors of the cells every time the value within the cell changes...
a
a
a
d
d
h
h
i
i
f
s

i need all the a's green and the d's yellow and the h's red again

the cells are cutomer names not letters

 

[Joe4]

i need all the a's green and the d's yellow and the h's red again

Red again? Where was red mentioned in the first place?
Are you alternating between two or three colors?

If you can make use of a "helper" column, I know of a way to do this.
Say your data begins in cell A1. Enter this formula in B1 and copy down for all rows:

=SUMPRODUCT((A$1:A1<>"")/COUNTIF(A$1:A1,A1:A$1&""))

Now, highlight all rows and select Conditional Formatting, and choose the formula option, and enter this formula in for condition 1:
=mod($b1,2)=1
and select your green color formatting.
Now, add a second condition with this formula:
=mod($b1,2)=0
and select your yellow formatting.

This works for two colors. If you have three, you would just use three conditions, i.e.:
=mod($b1,3)=2
=mod($b1,3)=1
=mod($b1,3)=0