I will answer back to front, TNA not been there but you need the AIR files, they have an index on line search for mobilisation as my suggested starting point.
Accept whatever was on the production line NO- Contracts were placed for the AM by the MoS , contracts specified spec qty. MoS instructed Contractors on current applicable schemes.
colour etc had to be specified because some of a contract might be for Middle east use whilst others for home / Europe use.
MTP 46 was a War Office publication. but we know from photo evidence we followed the Army lead, There is an Army poster re application of Camo plus correct positioning of markings, The RAF had a poster Air Diagram 1382 which defined camo schemes to be employed, but to date a copy has never been located.
There might not have been an AMO instructing intro of camo, but it could have been a pre war secret letter that required its embodiment into unit/station war books / mobilisation procedures/orders - as I have stated previously For both GW 1 & 2 no DCI etc was issued instructions came by confidential or restricted signals. - Bryan Leggat is trawling the N series of AMO. TED.