The Hunter L*a*b* color scale evolved during the 1950s and 1960s. At
that time, many of the scientists involved with color measurement were
working on uniform color scales. The X,Y,Z system was being used, but
it did not give a good indication of sample color based solely on the
numbers. The uniform color scales being investigated gave better indications
of the color of a sample based solely on the numbers. There were several
permutations of the Hunter L*a*b* color scale before the current formulas
were released in 1966.
The Hunter L*a*b* color scale is more visually uniform than the X,Y,Z
color scale. In a uniform color scale, the differences between points
plotted in the color space correspond to visual differences between the
colors plotted. The Hunter L,a,b color space is organized in a cube form
similar to the CIE 1976 L*a*b*
The L* axis runs from top to bottom. The maximum for L* is 100, which
would be a perfect reflecting diffuser. The minimum for L* would be zero,
which would be black. The a* and b* axes have no specific numerical limits.
Positive a* is red. Negative a* is green. Positive b* is yellow. Negative
b* is blue.