+2  A: 

Try this:

<asp:Chart id="Chart1" runat="server">
  <BorderSkin BackColor="Transparent" PageColor="Transparent" 
    SkinStyle="Emboss" />
</asp:Chart>

The BorderSkin.PageColor and BorderSkin.BackColor properties should do the trick...

Jakob Gade
The PageColor property did the trick. Thanks a lot!
Antoine Aubry
Awesome, glad to help. :)
Jakob Gade