Private Sub Worksheet_Change(ByVal Target As Range)
Dim rCell As Excel.Range
Dim rCodes As Range
Dim vMatch

Set rCodes = Range("B2:B12")

If Not Intersect(Target, Range("O:O,R:R,U:U,X:X,AA:AA,AD:AD,AG:AG,AJ:AJ,AM:AM,AP:AP,AS:AS,AV:AV,AY:AY,BB:BB,BE:BE,BH:BH,BK:BK,BN:BN,BO:BO,BT:BT,BW:BW,BZ :BZ,CC:CC,CF:CF,CI:CI,CL:CL,CO:CO,CR:CR,CU:CU,CX:CX,DA:DA,DD:DD,DG:DG,DJ:DJ,DM:DM,DP:DP,DS:DS,DV:DV,DY:DY,EB:EB")) Is Nothing Then

For Each rCell In Intersect(Target, Range("O:O,R:R,U:U,X:X,AA:AA,AD:AD,AG:AG,AJ:AJ,AM:AM,AP:AP,AS:AS,AV:AV,AY:AY,BB:BB,BE:BE,BH:BH,BK:BK,BN:BN,BO:BO,BT:BT,BW:BW,BZ :BZ,CC:CC,CF:CF,CI:CI,CL:CL,CO:CO,CR:CR,CU:CU,CX:CX,DA:DA,DD:DD,DG:DG,DJ:DJ,DM:DM,DP:DP,DS:DS,DV:DV,DY:DY,EB:EB")).Cells

If Len(rCell.Value) > 0 Then

vMatch = Application.Match(rCell.Value, rCodes, 0)

If IsError(vMatch) Then

MsgBox "Invalid code selected"

Else

rCell.Offset(, 1).Interior.Color = rCodes.Cells(vMatch).Interior.Color

End If

End If

Next rCell

End If
End Sub

Option Explicit
Private Sub Worksheet_Change(ByVal Target As Range)
' This code checks for a change of Status in the Status column and
'   on change fills the adjacent Cost cell with appropriate colour then
'   enters current date into the adjacent Date cell.
' The range covered extends from column ‘R’ (first Status column), to column ‘EZ’ (last Status column).
' If adding columns adjust ranges accordingly!

    If Target.Count > 1 Then Exit Sub
    With Application
        .ScreenUpdating = False
        .EnableEvents = False
    End With
    Dim rCell As Range
    Dim rCodes As Range
    Dim rRow As Range
    Dim vMatch
    Set rCodes = Range("E2:E12")
    If (Target.Column >= 18) And (Target.Column <= Range("EZ1").Column) And (Target.Column Mod 3 = 0) Then
        If Len(Target.Value) > 0 Then
            On Error Resume Next
            vMatch = Application.Match(Target.Value, rCodes, 0)
            If IsError(vMatch) Then
                MsgBox "Invalid code selected"
            Else
                With Target
                    .Offset(, 1).Interior.Color = rCodes.Cells(vMatch).Interior.Color
                    .Offset(0, 2).Value = Date
                End With
            End If
        End If
    End If
End Sub