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Any sight that could be described as yellowish or bluish is called an inorganic chromatic visual sensation. We use words like yellow, blue, gold, cyan, indigo, brown, orange, violet, turquoise, chartreuse, azure, ocher, cerulean, sepia etc. to identify particular visual sensations within the inorganic category. Ewald Hering reports that, "no color is both yellowish and bluish … yellowness and blueness are mutually exclusive."¹ Therefore inorganic visual sensations are susceptible of binary description. The reference experience for inorganic chromatic sensation is seeing gold. So to make a binary description of an inorganic chromatic sensation, compare it to seeing gold. Report the result using one of the following algebraic statements. If the two experiences are not comparable, then say that the sensation is not an inorganic chromatic sensation and express this as $\delta_{e}=0$. If the sensation is like seeing gold, then say that it is yellowish. Express this as $\delta_{e}=+1$. If the sensation is not like seeing gold, then say that it is bluish and that $\delta_{e}=-1$. The number $\delta_{e}$ is called the yellowness.

Summary

Noun		Definition
Inorganic Visual Sensation	$\sf{\text{Any yellowish or bluish visual sensation.}}$	1-14

Adjective		Definition
Yellowness	$\delta_{e} \equiv \begin{cases} +1 &\sf{\text{if a visual sensation is yellowish }} \\ \; \; 0 &\sf{\text{if a sensation is not yellowish or bluish }} \\ -1 &\sf{\text{if a visual sensation is bluish }} \end{cases}$	2-4