This provides a geometrical interpretation of critical points of a function of three variables. You can use the hotspot in the - window to move around the turquoise point in the 4D Color Graph and the slices. The color graph is colored according to the value of the , and -partials at that point. If the x-partial is positive, then the point is colored red; if the y-partial is also positive, then a blue layer is added, and if the z-partial is also positive, then a yellow layer is added. At a point where a partial is zero, we can observe a transition of color.

A critical point is a point where all three partials are zero, so it's a point where we observe a change of color in every direction. Hence, it must be a point where all eight colors meet.