^ I am not a paint expert, especially not robotic paint application at a car factory, but am led to believe there are a lot of factors that determine the visual color and sheen of the same paint on different surfaces such as whether it was the same batch of paint, humidity, static on plastic surfaces, texture of the plastic, rate at which the paint can be applied, distance of application around sharp curved areas, etc. This is especially true with metallic paint.
More to the point, why would they deliberately make a color very similar yet try to make it any different like it's not a perfect match? That's not what I see on the many different '98 Mountaineer pictures I found online. At most I would suspect that they put some fortifying agent in the paint on bumpers, trying to make it more chip resistant, or a different primer that works better on plastic.
Paint shops can make up test cards for their mix and then they or you can hold them against the vehicle and decide which to go with.