According to Fletcher's books, only "some" tanks of A and C Companies were fitted with this roof screen. So if you want to use the screen on your model you're limited to those units.
As for colour, well who knows? In one photo of a camouflaged A Company tank the colour of the wood appears closer in tone to the ochre colour of the camouflage than the darker colours, suggesting unpainted wood.
I would be surprised if they were painted as they seem to have been produced in a hurry and in limited quantity. But I think it would be difficult for anyone to say you're wrong either way.
It's a shame no Mk1's were actually fitted with the original anti-grenade solution, a 4mm perforated applique plate raised 12" (300mm) above the normal roof. 25 sets were produced and some tanks were built or fitted with mounting studs for them, but none were ever fitted. The wood and wire frames were made as a quick alternative solution.