Look at a plain old pearl bait...the whitish colored ones. Pearl powder added to you plastic will "pearl" whatever color the plastic is. A common pearl color is pearltreuse, a pearled chartreuse. Pearls work inside the baits all the way thru and tend to turn even clear colors to opaque colors.
Hi lite is added to the plastic to give the surface a "sheen", like an oil slick on water. While in the same family as pearls, the hi lite does its work on the surface of the bait even though it is present all the way thru a bait. I have pearl powder and liquid but I use way more hi lite that pearl and by adding lots of hi lite you can achieve about the same thing as a pearl but with way more character to the color.
Pigments are colorants. Most are liquid, there are a few that come in powdered form though. I use only liquid.
All of these elements have to be "experienced"....our telling you simply will not teach you how each behaves in plastic. You have to actually make the plastic and see how the use of these products unfolds. The learning here is fast and even a messed up batch of plastic will have some use down the road.