VBA-highlight cell(s) in a column range if empty or greater than a value

[mcinvalek]

I am using Excel 2010 (x32). I am new to VBA and trying to create some VBA conditional formatting to be used as data validation. The first column is a data column. I want to fill a cell red if it is empty or orange if the cell is greater than a value in cell B4 on another sheet named "Instructions". I have created the following but it is not working. Any suggestions? Also, instead of the named range of "A2:A2552", can I use a do until or do while loop to accomodate a growing range?

Private Sub Worksheet_Change(ByVal Target As Range)
    Dim icolor As Integer
    Dim cell As Range

    If Intersect(Target, Range("A2:A2552")) Is Nothing Then Exit Sub

    For Each cell In Target
        icolor = 0
        Select Case cell
            Case Is > Range("Instructions!B4"): icolor = 3
            Case "": icolor = 45
        End Select

        If icolor <> 0 Then cell.Interior.ColorIndex = icolor
    Next cell
End Sub