Chinstrap is quite correct in khaki web. The leather version was an earlier iteration. Both are fine for WW2. As you can't see the inside of the chin cup, I don't think you need to paint it natural leather. 
Cuffs could but not necessarily should be khaki knit. Individuals usually sewed the tops of socks to the cuff to keep the breeze out.
It's not a webbing chinstrap on that figure it's a leather one, the webbing ones dangle different when unfastened. If you unfasten this one you can take it off yer melon, if you want to go all dangly you've got to unbuckle it from the rim too. The devil's in deetail... just so you know old chap.

With the webbing chinstrap it was far easier to unbuckle it then pull it up over the helmet, like the bloke in this famous piccy...

Look at his mate on the right, with leather chinstrap...
and much light will enter into yer darkness!