How to look for empty cells in a range using vb?

So you're trying to set font to green for all rows which contain a blank cell within the used range, right?

Sub foo()
Dim c As Range
For Each c In ActiveSheet.UsedRange
    If c.Value = "" Then
        c.EntireRow.Font.ColorIndex = 4
    End If
Next c
End Sub

This works for me...