Have now altered the code to this:
Private Sub ATCST_AfterUpdate()
Dim Arr As Long
Dim WNB As Long
Dim Wht As Long
Arr = RGB(231, 244, 66) 'Colour Code is #E7F442
WNB = RGB(0, 255, 0) 'Colour Code is #00FF00
Wht = RGB(255, 255, 255) 'Colour Code is #FFFFFF
If Me.ATCST = "Arrived" Then...