This representation of the Lab colour space often found on the net is not correct:
(Link: Google image search for "Lab colour space)
The complete derivation of the Lab colour space can be read well at Wikipedia, here only the further consideration: The outer envelope is formed by the colours of maximum saturation. These are spectral curves in which one or more measured spectral ranges reach the maximum. If one now calculates the Lab colour values for numerous such spectral curves and displays them three-dimensionally, the result is a very irregular, laterally lying drop-shaped colour body.
Here is the calculation of approx. 2000 edge colours according to the above consideration and the representation by Bruce Lindbloom.
