You can try it This way.
First create an running total or formula which increments by 1 when placed in detail section,Finnaly which will give you the Count of Total Records.
If there are 4 records in Detail section .
If you have placed that formula Say "Count" in detail section,Then
In Detail Section it displays like
1
2
3
4
so this will be your output.
Now you want to color it Alternately
To fullfill your requirement , you will have to
go to "Select Expert" or "Format Section" by rightClick on the section head.
Click Detail Section
Now Click on "Color" Tab on right.
Make Check to the BackGround Color
click on X-2 and Insert this formula
Then save it and Run the report.
You will get your alternate colored report.
Enjoy Crystal Reports.
Regards
Keval Raj