Private owner mineral wagons were requisitioned by the Government on the outbreak of war in 1939 and never handed back. By 1952, none of them had been painted for at least a dozen years and they were getting pretty faded. "Modernisation" at this date meant breaking up wooden chassis 13T minerals with grease axle boxes and replacing them with all-steel 16T minerals with oil axle-boxes. The replacements were still unfitted... Quite a few wooden PO mineral wagons built on pre-grouping days , often to 10T capacity , were still in traffic in 1948

Wooden PO minerals were fading fast in the 1950s (literaly! )- quite a lot of our knowledge of the liveries comes from those chasing the survivors with camera and note book to record examples that were still fairly clear

It was BR policy not to repaint wooden minerals. Ever. They were on their way out, everything was scarce - why waste paint on them? The ironwork was probably given an occasional lick of paint - the wood simply weathered to unpainted (There was a brief period where policy was relaxed and minerals were painted grey - but it was very brief)

PO vans were pretty uncommon. Vans were almost entirely the prorogative of the railway companies. I'm pretty sure Fyffes did not have their own vans - pre-nationalisation the ships came into Hull, then Southampton or Avonmouth and were moved in LNER or SR banana vans.So the Fyffes and Colmans vans are pretty certain to be inauthentic (Banana vans were special vehicles, fitted with steam heating, fitted underframes, XP , for fast perishable traffic. And they generally moved as trainloads from the ports to stores). Bass probably did have their own vans but they probably didn't venture outside Bass' own internal railway network.

So my first step towards a more authentic fleet more in period involves a paint brush (a fine one as it's N). I would put Fyffes and Colmans into BR fitted bauxite (a bright orangy shade in the 1950s) and BR unfitted grey (in the 1950s a pretty light shade, very different from your dark grey van).They will still be quite distinctive in colour. Bass and OPCM can be left

The minerals are a weathering job. Bullcroft is an entirely authentic PO livery for a major S Yorks colliery . But it needs fading with a thin pinkish wash (including the white letters) and then a light application of a dirty wash . Dombey ~& Sons has more to do with Dickens than the coal trade I suspect. That might be a target for repainting as weathered unpainted greyish wood

Some prototype reference  PO mineral 1950s   replanked PO mineral  Stanton mineral NRM per/post restoration

and my search turned up this gem You tube - Coal and the War (1941)  though the date means that the wagons seen are still pretty pristine