You can use
GridView
's
RowDataBound
Event like this:
protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.DataRow )
{
double salary=0.0;
salary= double.parse(e.Row.Cells[1].Text;
if (salary>=5000)
{
e.Row.Cells[1].BackColor=System.Drawing.Color.Red ;
}
}
}