Try something like this (but it doesn't handle a single ' character):
Code:
Sub validate()
Dim lastRow As Long
Dim i As Integer
Dim testVal1 As String
Dim testVal2 As String
Dim counter As Long
lastRow = Range("af" & Rows.Count).End(xlUp).Row
For i = 3 To lastRow
testVal1 = Range("af" & i).Value
If testVal1 <> "0" And testVal1 <> "1" And testVal1 <> "'" Then
Range("af" & i).Interior.Color = vbRed
Range("af" & i).Font.Color = vbWhite
counter = counter + 1
End If
testVal2 = Range("ag" & i).Text
If testVal2 <> "0" And testVal2 <> "1" And testVal2 <> "'" Then
Range("ag" & i).Interior.Color = vbRed
Range("ag" & i).Font.Color = vbWhite
counter = counter + 1
End If
Next i
End Sub