How to highlight invalid data on gridview if validation against a DataTable is failed VB.Net?

I tried my best to shrink down the program to the following code. In this example, I have UK and USA as valid countries. If someone lives outside those countries, I wanna show an error message and highlight them on the gridview. For example, John and Chris are from China so they should be highlighted on the gridview. Is it possible to do that ? Please see example picture. Either just Name or the whole row can be highlighted.

Thanks a lot.

    Dim dt As New DataTable
    dt.Columns.Add("ID")
    dt.Columns.Add("Name")
    dt.Columns.Add("Country")

    dt.Rows.Add("1", "John", "China")
    dt.Rows.Add("2", "Harry", "USA")
    dt.Rows.Add("3", "Joe", "UK")
    dt.Rows.Add("4", "Emma", "UK")
    dt.Rows.Add("5", "Chris", "China")
    dt.Rows.Add("6", "Jenny", "UK")


    Dim isValid As Boolean = True
    Dim keywords() As String = {"UK", "USA"}
    Dim str As String = ""

    For Each x As DataRow In dt.Rows
        If Not keywords.Contains(x("Country").ToString()) = True Then
            isValid = False
        End If
    Next

    If isValid = False Then
        lblmessage.Text = "Some people don't live in valid countries"
    End If

    GridView1.DataSource = dt
    GridView1.DataBind()

Is it possible to do that ?

Yes, one way is to use GridView's RowDataBound event. Assuming you have a list of valid countries:

Private validCountries() As String = {"UK", "USA"}

Protected Sub GridView1_RowDataBound(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewRowEventArgs)
    Select Case e.Row.RowType
        Case DataControlRowType.DataRow
            Dim row = DirectCast(e.Row.DataItem, DataRowView).Row
            Dim country = row.Field(Of String)("Country")
            ' assuming you're using TemplateFields with LblName for the Name of the user '
            Dim LblName = DirectCast(e.Row.FindControl("LblName"), Label)
            If Not validCountries.Contains(country.ToUpper) Then
                LblName.CssClass = "InvalidCountry"
            End If
    End Select
End Sub

If you're using BoundFields instead, you need to apply the CSS on the table cell

e.Row.Cells(1).CssClass = "InvalidCountry"