Odd Background shading behavior And Error Checking

Hello, I was hoping someone could tell me why, the code below is inserted in my worksheet, when multiple cells are selected and cleared by right clicking and selecting "clear contents" they are shaded the color for the "OFF" Case, but when the same steps to clear are performed on only one cell it remains white? Also if you could suggest some changes so that when the cells are cleared I do not get a Type Mismatch error, that would be great.

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

 On Error Resume Next
 
'change the conditions below
  Select Case Target.Value
           Case "OFF"
                icolor = 35
            Case "RTO"
                icolor = 8
            Case "vacation"
                icolor = 8
            Case "10-9 SBP"
                icolor = 38
            Case ""
                icolor = 2
            Case Else
        End Select
  
  Target.Interior.ColorIndex = icolor
 

End Sub

Thanks!
Clayton Grove