You can try it in graph customizing,in global settings were u can add line graph and different colors. pls have look at below thread .
Hope its useful to u,
Hi Rajesh ,
Pls Fallow Below Procedure...
->CLick On BG
->Click On Customization
->Select Series->Rc Add Series->Maintain customizations in that series..
->Back to BG. ->Select Simple Series and select customizingID- Mention Series Name here...
Then It Automatically changes reflects to your BG...
Another Way is Pls Fallow below link...