Hi Russell,
Very nice build, one of my favourite subjects

The things that come to mind that could be added are:
- the sand shield fittings,
- a board or rail between the track guards (fender thingies) so the jerry cans etc can be stored on the front of the vehicle,
- most NZ Shermans had some form of stowage on the rear plate, be it a large bin similar to the one on the turret and/or ammo boxes and/or jerry can.
As for colour, I would go with either “Light Mud” and “Blue/Black” like the colours on the vehicle in the Tamiya Magazine your Sherman is on, or Olive Drab either the US version or the British S.C.C. 15. Time wise, the colour switch seems to have taken place around mid 1944 after the Battle of Cassino, but having said that, a few tanks were still in the Light Mud and Blue/Black scheme in Trieste at the end of the War.
I hope that is of some help.
Cheers
David