You cannot see details on black plastic in all the photos they would need. Admittedly they could just do grey for the promotional shots, but the cost would add up. Some things look better undercoated white, and being white on grey is also easier than white on black (if like me you don’t use half a can per batch)
I actually had a few Morian orcs made in black plastic. Don’t know why they were that way, but it’s not that big of a change. You will have to undercoat them anyway if you want a really good painted mini.
Colour doesn't determine price. If it did, then a TV set molded in a grey plastic box would cost less than the exact same TV if the box was molded in Black. And it doesn't work like that.
On top of all of this, you would have to add a lot more pigment to make it black than you do when it is grey, upping the costs of production.
Plastic comes in all colours and costs the same price. They don't add in a pigment to grey plastic to make it black. This isn't baking with food colours and white sugar. :D
If you've ever seen a plastic injection molding machine and know how it's operated, then you know that plastic companies buy shreaded plastic in pellets, put the pellets in the machine, which melts them, and then the liquid plastic is forced into the metal mold (Your model kit) at high pressures. Once the liquid plastic dries, the mold is poened and the plastic parts are taken out. Look for a video on You-tube. It's quite amazing.
Haven't you guys ever built any other plastic models besides Games Workshop ones? Like a tank (Molded in Green) or car (Molded in white, grey, black, red, yellow, blue, purple and tan.)?
Just be glad they don't mold them in red - White undercoat tends to go pink when sprayed over red plastic!
Tarrak 50 dollars bottle of top brand perfume costs less than a dollar to produce.
Colour of plastic models is a minor feature since stuff like elasticity and hardnes are more important.
Also the individual type of plastic ( color is just feature, chemical formulae determines the type) is part of production technology which is most likely bought by GW, and during the course of proces of acquiring the technology the decision makers dont look at the colour but at the costs, eficiency, (recently on ecological aspects) etc.
For modeling purposes grey is better, as it is equaly covered by black or white primer.
And using primer strongly improves the look of one’s miniatures.
I took a plastics Technology course back in the past and I don’t remember ever hearing about colour being a factor in price of plastic. It was usually like what Gar Shadowflame says - it’s the type of plastic.