Sub FindDupes()
Dim myRange As Range
Dim mySheet As Worksheet
Set mySheet = Sheet1
Set myRange = mySheet.Range("C1:C500") 'This is the range you want to process for dupes.
For Each cell In myRange
x = Application.WorksheetFunction.CountIf(myRange, cell.Value)
If x > 1 Then
With cell.Interior
.Color = 65535
End With
End If
Next
End Sub