Set Rowstyle for gridview backcolour e.g.
<asp:GridView id="gd" runat="Server">
<RowStyle BackColor="Red" />
</asp:GridView>
If u want it from Code side then
For particular Column
gridview.Columns[0].ItemStyle.BackColor = System.Drawing.Color.Red;
For grid
gridview.BackColor = System.Drawing.Color.Red;