Repainting a cell using excel VBA

Hello,
I am writing a code in excel VBA to generate a report.I am totally new to VBA.Here's my code

Private Sub CommandButton1_Click()
Dim a1 As Integer
Dim d1 As Integer
Dim r1 As Integer
a1 = Sheet1.Cells(2, 3)

d1 = a1 \ 8
r1 = a1 Mod 8

If d1 >= 5 Then

Sheet1.Cells.Range("A20:E20").Interior.Color = vbBlack

Else

For cnt = 1 To d1

Sheet1.Cells(20, cnt).Interior.Color = vbBlack

Next cnt

If r1 <> 0 Then

Sheet1.Cells(20, cnt).Interior.Color = vbBlack

Sheet1.Cells(20, cnt).Font.Color = vbWhite

Sheet1.Cells(20, cnt) = (8 - r1)

End If

End If
End Sub
..
The basic idea is to colour cells after the click of command button based on the value in Cells(2,3).Cells get coloured based on multiples of 8. The problem that I am facing is that the cells retain the colour permanently.
For example based on the value in Cells(2,3) if 5 cells get coloured ,they remain there permanently.When I change the value in cells(2,3) and click the command button repainting of cells does not take place.. Can anyone please guide me regarding this??

Thanks