The thing everyone forgets-- and I lose my mind with people talking LED colors for FX sabers... NONE of us are seeing the same thing ever. Keep in mind that a final film has gone through a color grading process that could make things look different from how they did in real life. Also, still film stocks work at different color temperatures. So to compare the final film to BTS stills from a variety of sources is not going to make for color matching if the color is one that is easily changed by light. Black is black, but warm colors, the yellow, red, brown space especially, can shift VERY easily. ESPECIALLY when you using a metallic paint which is going to have a degree of reflection.
Finally, each of us is looking at a monitor of some sort. I'm sure very few, if any, of us are using True Color systems to surf the web-- all of our monitors have color profiles. Some of us like brightness cranked, I'm sure others don't. Some people have a better color range detection ability in their brain than others. We're never going to all see the same thing.