> I cannot find similar rolls of plastic that are white.  Why not ?

Don't know if it's relevant but I've found white doesn't stand
up to UV very well and falls apart long before black or clear.
I presume the filler in white is, or something like, TiO2 and in
black would be carbon. That said, I get wood delivered in
white plastic wrap, quite thick, printed with the company stuff,
so it is made. I re-use it, but see above re longevity outdoors.
You might try a lumber yard or factory and track it back from
there. Possibility of a spoiled roll going cheap ?

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