how to change row color of gridview if condition is true ?

if u get the data from database query then u should write query like 'select columns,case when status='on' then 'R' else 'Y' end as cl from tbl'.. then bind the grid..

then in gridview write item template like this:

<asp:GridView runat="server" ID="grd">
           <Columns>
               <asp:TemplateField HeaderText="Header1">
                   <ItemTemplate>
                       <asp:Label runat="server" ID="lbl" CssClass='<%#Eval("cl") %>' Width="100%" Text='<%#Eval("ID") %>'></asp:Label>
                   </ItemTemplate>
               </asp:TemplateField>
           </Columns>
       </asp:GridView>

Then Write Style Sheet like This:

<style type="text/css">
        .R
        {
            background-color: Red;
        }
        .Y
        {
            background-color: Black;
        }
    </style>