It's a US regulation regarding the transportation & sale.
The Code of Federal Regulations Title 15, part 1150.2, states "no person shall manufacture, enter into commerce, ship, transport, or receive any toy, look-alike, or imitation firearm" without the requisite blaze orange marking. A waiver may be obtained (1150.5) by the theatrical, movie, or television industries.
It currently has no bearing of law in any other country in the world. I get this question in my store all the time.
ASC Age Verifier for Red Deer & Area Alberta