Try this on your latest attached file while OB4 is the active sheet:
Intersect(Range("B13").CurrentRegion, Range("E:E,G:G,I:I,K:K,M:M,O:O,Q:Q,S:S,U:U,W:W,Y:Y,AA:AA,AC:AC,AE:AE,AG:AG,AI:AI,AK:AK,AM:AM,AO:AO,AQ:AQ,AS:AS,AU:AU,AW:AW,AY:AY")).SpecialCells(xlCellTypeConstants, 1).Offset(, 1).FormulaR1C1 = "=R20C34-RC[-1]"
If you want plain values instead of formulae it's more long winded:
For Each cll In Intersect(Range("B13").CurrentRegion, Range("E:E,G:G,I:I,K:K,M:M,O:O,Q:Q,S:S,U:U,W:W,Y:Y,AA:AA,AC:AC,AE:AE,AG:AG,AI:AI,AK:AK,AM:AM,AO:AO,AQ:AQ,AS:AS,AU:AU,AW:AW,AY:AY")).SpecialCells(xlCellTypeConstants, 1).Offset(, 1).Cells
cll.FormulaR1C1 = "=R20C34-RC[-1]"
cll.Value = cll.Value
Next cll
(Doesn't look at the colour of the cells, merely looks for a number.)