How to change the column's cell Color based on condition

want to change color of my Achievement column based on condition like If(Achievement>95%) it will show green color in cell.How to to do it?
My aspx code:

<asp:PlaceHolder ID = "PlaceHolder1" runat="server"/>

Code Behind:

DataSet ds = new DataSet();
        ds = new ProcessedData().LoadAllData(Convert.ToInt32(ddlYear.SelectedValue), Convert.ToInt32(ddlMonth.SelectedValue), Convert.ToInt32(ddlDepot.SelectedValue), ModuleID);

        StringBuilder strResults = new StringBuilder();

        strResults.Append("<table border='1' style='width:628px'>");

        strResults.Append("<tr style='background-color:gray; color: White;'><th>Description</th><th>Target</th><th>Actual</th><th>Achievement</th></tr>");

        if (!object.Equals(ds.Tables[0], null))
        {
            if (ds.Tables[0].Rows.Count > 0)
            {
                for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
                {
                    strResults.Append("<tr style='color: black;'>");
                    strResults.Append("<td>" + ds.Tables[0].Rows[i]["Description"] + "</td>");
                    strResults.Append("<td>" + ds.Tables[0].Rows[i]["Target"] + "</td>");
                    strResults.Append("<td>" + ds.Tables[0].Rows[i]["Actual"] + "</td>");
                    strResults.Append("<td>" + ds.Tables[0].Rows[i]["Achievement"] + "</td>");
                    strResults.Append("</tr>");
                }

                strResults.Append("</table>");
                PlaceHolder1.Controls.Add(new Literal { Text = strResults.ToString() });
            }
            else
            {
                strResults.Append("<tr>");
                strResults.Append("<td align='center' colspan='4'>There is no Record.</td>");
                strResults.Append("</tr>");
            }
        }