This is black, it should look the same as a milspec lower receiver.
It's not a dark black like a standard milspec receiver. It's more like a dark grey/greyish black. Compared to my receiver and factory end plate, you can absolutely tell the difference in color . . . Not that that's a bad thing b/c I wanted the contrast.
I'm not sure if it's some sort of optical illusion because of the background color, but the four pictures of the single end plate provided by OP have a greenish tint to them, while in the picture of five of them on top of some wood the color is very accurate in my opinion.