Internal ring presents master color. 
Diagram explains how colors in segments and inner circle are changed. 

If "L* Change" parameter is to "none" internal circle is invisible. 

Easy Mode: pastel colors set (screenshot)

Easy Mode: neutrals  (screenshot)

Advanced mode:

ENTER TOOL 

Tips how to learn more.

1. Switch presets to learn about relationship between color saturation and perception 
2. Notice relationship between color hue and perception.
3. Observe how changes in L* are perceived - L* unchanged vs. changed
4. Compare differences for various formulas ( e.g. dE 2000 vs. dE 1976 or CMC)
5. Compare visual appearance for "isolate" function on and off
6. Observe influence of background  - how it change perception
7. Switch on details and analyse what happen if sample go out of working colorspace
8. Perform your exercise once early in the morning and repeat it at the evening.