Use a Select case
statement.
This is much cleaner to do a lot of this sort of thing. You can have options which then effectively do a large if/elseif statement like you are trying to do but the code works a lot better (and is cleaner).
See this link for more documentation.
Here is what will work for your situation:
Select Case Me.txtArtikelStatus
Case "05"
Me.txtArtikelStatus.BackColor = RGB(215, 228, 188)
Case "01"
Me.txtArtikelStatus.BackColor = RGB(219, 238, 243)
Case "06"
Me.txtArtikelStatus.BackColor = RGB(252, 213, 180)
Case "08"
Me.txtArtikelStatus.BackColor = RGB(252, 213, 180)
Case "09"
Me.txtArtikelStatus.BackColor = RGB(252, 213, 180)
Case Default
'this captures everything else
End Select