Keep in mind you are adding these powders to plastic and not mixing paint. A four ounce batch of clear plastic will go opaque in a heartbeat using these auto pigments if you add too much, just like regular hi lites. Since the plastic we use is not a part of any automotive paint process, but can be used by us, we have to find the balance in its use. Small additions, slow going is the rule here. To use these in plastic, forget about the mixing or undercoat requirements the paint side asks for.
The top coat is what I use most of for getting a hi lite into plastic. In an automotive use, the top tops are merely a clear coat that carries the pearl pigment and they are applied of the actual color to create a color illusion, much like hi lites do in the plastic. They will make a clear plastic a solid color when mixed to strong and the color pigments will bleed into clear plastic if mixed strong and solo. If this happens to you, you'd gone too far with it. In a clear coat paint, this color is so thin that it doesn't hardly appear noticeable.
Because this pearl pigment powder mixes with any liquid, it is a great way for the air brushers to trick out finish coats. A friend of mine owns a body shop with his dad and took on a paint job of a custom built stunt plane. The plane's paintable parts were brought in before they were assembled. The base coat of paint was a gold metal-flake that had a deep transparent red shot over the top as the primary color. The top coat, the one using the pigments we are discussing here, was really bright tangerine [orange] color. The end result was amazing in the sun. I have never seen any paint come with so many colors simply from a few coats of paint. The same effects could be gotten by making plastic red with gold glitter and then clear coating with a thin tangerine colored pearl powder mixed as a thin hi lite top coat. As for eyes, I have no idea if the clear with the thin pearl would be a factor but assume so.
I have lots of different pearl powders simply because I love to play with color. Sometimes I come up with a great finish result. Lots of times its a flop. Each flop is a lesson though. The biggest lesson I have learned thus far is that a very little of the pigment is needed to twist the heck out of a colored plastic. Its hard to stress enough that so very little is needed to get the job done and most often is what discourages people using this powder. Whatever it says on the product pages for ordering, scrap it. This is used in an entirely different way and in a different catalyst. The top coat colors is what you want only because the powder's talc-like quality is so fine that it creates an illusion of color without actually changing the color much.