Couple things here regarding the question. First, by adding the pigments to plastic to get the colors to work as well as they do brushed on its would take an incredible amount of the pigment. Brushing it on requires so very little of it it's unreal. When brushed on over a clear plastic one can see how little of the pearl is actually on the baits as these seem almost transparent like the base coat: add light and change angles and you'll see how much so little can affect the actual color of the plastic. Secondly, just about every color shown is used in a clear top coat over a base color in the realm from which they were ordered from: auto paint industry, nail polish industry. Some of the pigments actually are added to colored paints or polishes, but like in plastic they can't even begin to shift colors like having the pigment as the top coat.
Another problem that arises with adding these color shifting pearls to the plastic directly is that they all have color pigments in them and will stain any color of plastic you put them in and sometimes its not pretty. I've applied these color shifting pearls over white, clear, purple and black plastic. Clear plastic that's been brushed yield some of the most natural looking minnow baits I have ever seen, let alone made, but they are pale [literally] by comparison to those with a dark color underneath. I haven't found a color shifting pearl I like with white plastic so no pics using that as a base color. My transparent purple will allow light to move thru the pearl top coat at certain angles that make a bait appear as though there is nothing on it at all, but this illusion is one I haven't been able to capture on a camera yet, video either. The shift is just a blink but there. Black reigns supreme. While all other base colors reflect at least some light they tend to mute some of the shifting by sending light back thru that coat. Black sucks up any light that hits it. Being atop of the black base the only light being reflected in in that top coat which greatly intensifies its pearl contents.
Powder paint is another example one can use to see how these pearls work. Paint a head with about any color, then re-coat it with a clear that's been spiked with the color shifting pearl products and you'll get exactly what the custom auto paint industry wants these pearls to do. One of the most dramatic paints I ever cooked up was using clear powder paint and adding a four-color shifting pigment of primarily light colors to it in an exaggerated amount and when applied to a black jig it is almost cosmic. When I mixed the same pigment into black powder paint about 90% of the effectiveness of the color shift was lost. A friend of mine owns a body shop and was asked to paint a custom stunt plane. The plane came in pieces and was painted a fire red, then finished with several clear coats having a gold/orange color shifting pigment added, then assembled when the painting was done. The result was stunning. As the plane passed in the air it went from red/to orange to gold....all in a flash.
I have 13 packages of pearl colors that are standard colors, not color shifting, and that are not like the colors that are found where plastic is sold. If we ever get out of this tundra weather I hope to use some of these both in clear plastic and in plastic of similar colors to the pigments. These will stain the plastic big time and is why colors will have to coordinate to some degree. As for the color shifting pearls, in my world they have but one place and that's on the surface of a base color.