First, Ive seen their plastics both on my calibrated monitor, AND IN PERSON,
at the Allentown show.
2nd, even if your monitor is not calibrated well... and you shift the values of All the colors at once... then they still all match. They are just darker or lighter.
However, if one color is seriously off due to improper matching, it stands out. It stands out no matter what you do to your monitor. It stands out in the game like a Blue LED pointed right at your eye.
Heres a simple Pictorial Example:
On the left side, we have a group of colors arranged by their Color and Value.
The color being from left to right, and value from V1 to V5.
We will ignore saturation and other aspects to be simple. Also, we will call the entire row of colors in a value, a "Family".
In example A & C, we can see they are entire families, and thus all the Values match.
However, in Example B, the first and 7th colors are Not from the same value levels... and so you can see that they stick out at bit. Especially when compared to A & C.
Example D shows the same, and shows the main family (green line), & the alternate values (orange lines).
And finally, example E, which is much easier to notice due to the extreme levels of value changes.
Of course, this is only a simple example to do with value, and does not even touch on the much more advanced aspects.
Edit:
If you play with various art programs on the PC, such as Photoshop, you can see a section of both a color wheel... and a color Swatch section. One thing you start to realize, is that picking the right colors is almost a mathematical thing.
In windows, there are 3 main colors: Red Green Blue. And each color can have 16 values. If we take a single dot (pixel), it could be: 0,0,0 which would equal Black. OR 16,16,16 which would be white. For Red, it would be 16,0,0. To make pink: 16,10,10.
This is important, because when you arrange a swatch palette, you often would be altering the colors values by a mathematical formula. For example, changing each color by adding +2. IE: 2,4,6,8. If you made a mistake... you could spot that color because it shows up against the rest of the colors.
Its much like Music. If you play the wrong note in a sequence, its going to be noticeable. Music is also very mathematical btw.
In the next picture, we can see various color swatch palettes in photoshop.
As we can see, the bottom left corner is a Pastel palette, and looks completely different to the bottom right Palette. If you did a Pastel painting, and dropped a color from the other bottom right palette in there.. it might look very out of place.
(unless the palette is very wide in contrast and depth)