Option Explicit

Sub UnfixedDate()
    Dim IroData
    IroData = "MMDD"

    Dim WS_Count As Integer
    WS_Count = ActiveWorkbook.Worksheets.Count

    Dim I As Integer

    Dim cell
    Dim position

    For I = 1 To WS_Count
        For Each cell In ActiveSheet.UsedRange.Cells
            position = InStr(1, cell.Value, IroData)

            Do Until position = 0
                If position > 0 Then
                    cell.Characters(position, Len(IroData)).Font.ColorIndex = 3
                    position = InStr(position + 1, cell.Value, IroData)
                End If
            Loop
        Next
    Next I
End Sub