Hong Kong SG335a 1975 Birds Missing Brown with RPS Cert U/M (toned)

There is an RPS cert when this was in a pane (I will include a copy) saying missing Crimson. SG list it as missing brown. SG say the missing Brown colour causes the bird to appear in the green underlay colour (Cat at 900 pounds) I have included a scan of a normal stamp (not included). This is toned due to poor storage (probably after there were certified)