The way my PC guy just explained it to me was like this..
A flat piece of material just takes a single pass to coat.
A round piece takes several passes to coat.
This affects the color.
We did my brother's chassis and it came out a lot darker than we wanted due to the amount of passes to coat round tube.
So, we ended up picking out another color, that was considerably lighter, to help compensate for this.
Also, I would not trust too many of the customer's color samples on the Prismatic website.
Some of those look fucky to me. And lighting will also play a role in the color's true color.