Not tested, and done from memory

"Row" is a VBA key word, but I think the real problem was that "EntireRow" was not qualified, i.e. it should have been something like rCell.EntireRow

Try

For Each rCell In ActiveSheet.Range("A4:A93").Cells
    With rCell.EntireRow
       If .Hidden Then
          .Hidden = False
          .Interior.colorIndex = 19
       End If
    End With
Next