The red line is the rate of the stiff part of the spring. The suspension bottoms out before the spring, so that one never goes to infinity.

The blue line is the combined rate, or the rate of teh whole spring in stock form. Note that the rate changes from an average of the two rates (red and green) to the same as the stiff part at the point that the soft part bottoms out.

The pink line is what it would look like if you trim the soft end of the spring, note that the bend has moved to the left.

The light blue line is if you cut the stiff end