Changing colors of the backround

[uniden32]

I currently have a timer routine that counts down from 30 minutes. I display the current time remaining in the countdown, as it counts down.

What I would like to do is have it change the color of the backround for that cell when the timer hits 30 seconds left, then 15, then 5, then every second after that until it hits zero.

Here is the code I'm using (courtesy of VoG and a few alterations)

Dim NextTick As Date

Sub StartTimer()
With ThisWorkbook.Sheets("Data").Range("D2")
    .NumberFormat = "hh:mm:ss"
    .Value = Time
End With
Call FormatTime
Call TickTock
End Sub

Private Sub FormatTime()
With ThisWorkbook.Sheets("Sheet1").Range("D4")
    .NumberFormat = "mm:ss"
    .Value = ThisWorkbook.Sheets("Data").Range("E3")
End With
End Sub

Private Sub TickTock()
With ThisWorkbook.Sheets("Sheet1").Range("D4")
    .NumberFormat = "mm:ss"
    .Value = ThisWorkbook.Sheets("Sheet1").Range("D4")
    .Value = .Value - (1 / 86400)
    If .Value <= (1 / 86400) Then
       Beep
       Call StopClock
        With ThisWorkbook.Sheets("Data").Range("H2")
            .NumberFormat = "hh:mm:ss"
            .Value = Time
       End With
       Call StartTimer
    End If
End With

NextTick = Now + TimeValue("00:00:01")
Application.OnTime NextTick, "TickTock"

End Sub

Sub StopClock()
On Error Resume Next
Application.OnTime earliesttime:=NextTick, procedure:="TickTock", schedule:=False
On Error GoTo 0
End Sub

Here is the image of the timer:

http://img98.imageshack.us/i/timerscreenshot.gif/

As always, thanks for any and all help.

Ralph