Pigment is the finely ground colorant that gives a colored pencil its color. Pigments are mixed with binders and other ingredients to form the pencil's core.
From the beginning of art, pigments have been quite literally “animal, vegetable, or mineral” direct from nature. Advances in chemistry have replaced a lot of the biologic pigments and invented thousands of new pigments.
Pigments are generally opaque. Dyes are the opposite and are transparent color.
Pigment load refers to the amount of pigment in a pencil's formula relative to its other ingredients.
A higher pigment load does not automatically produce stronger color because pigments vary in strength. The binder formula and how well the pencil lays down color also influences the final result.
Because colored pencil formulas are proprietary, exact pigment loads are unknown to consumers. Color intensity alone is not a reliable way to determine how much pigment a pencil contains which means most reviewers talking about “pigment load” and “highly pigmented colors” have no proof of the claim.
In the Lab, I’m careful to qualify that a pencil acts like something highly pigmented or appears to have a low pigment load but it’s really just an educated guess based on 30+ years of pencil usage. I’ll leave it to the pencil chemists and product engineers to define actual pigment loads.