They claim that "[t]he colour gradients are perceptually uniform and ordered to represent data both fairly, without visual distortion, and intuitively", however on my calibrated screen many gradients are visibly biased with non-uniform gradients, especially near the darker end. Most noticeable examples include "batlowK", "lipari", "navia" and even "grayC" which is a grayscale gradient.

edit: missed a part of the quote