Title: Similarities of colors with circle constraint

Source: Ekman (1954) and Borg and Groenen (1997, 2005)

Description: Similarities of colors with wavelengths from 434 to 674
nm. One extra object is introduced to simulate the center. There are
two similarity matrices: one contains the original data with missings
to the center object, the other contains a constant value between all
objects and the center object with the rest of the similarities
missing. The colors are (in nm):

434
445
465
472
490
504
537
555
584
600
610
628
651
674