there was certainly white camoflage items issued as i have a photo of a ski patrol in Manchuria and there all wearing white jackets and trousers.
that photo you have might actually be there helmet covers turned inside out then attached to their helemts as the helmet covers were lined in white cotton. im not saying thats what it is but its a possibility mate.
i would be surprised if the helmet covers were only in use during WW2. afterall the Japanese adopted steel helmets back in 1930 and looking at the ones in your photo, their very uniform and neat for field improvisations
found photo evidence of a large use of white cloaks and also further evidence that ski patrol troops were issued white uniforms including white puttees, trousers and tunics.
It also appears the white helmet covers were in use in China prior to WW2