http://mononodes.com/color-shift-dctl/

  Our DCTLs are offered in two distinct models: the “T” and “Non-T” versions. The “T” in our labels stands for the Tetra model, which adjusts across six hues—RGBCMY. On the other hand, DCTLs without a “T” employ cone-shaped, cylindrical, and spherical-shaped color models that differ subtly in their approach. These models include an additional specific adjustment for “Skin” hue. It’s important to note that neither model is superior to the other; they simply utilize different mathematical methods. The choice between Tetra and Non-Tetra often depends on personal preference as each provides unique results.