Did You Say "Yellow"
Donald H. Voss
Vienna, Virginia

Because of differences in computer software and hardware (including the various phosphors used in monitors), there is an excellent chance that the color of an image created by one computer will differ from the color displayed on another computer to which that image has been transmitted.

Specialized equipment, software, and expertise can reduce such differences, but these are beyond the reach of most viewers. And, indeed, color concepts held by many people are highly subjective. In the circumstance, developing a common understanding of color terms and definitions is essential to useful discourse. The following note illustrates some situations encountered in applying the hue-name "Yellow" to azalea flower color.

Yellow - like "all the little bits and pieces" of an old commercial - "it's in there!" The key question is often "how much?" In the case of many deciduous azaleas, the answer is "a lot" primarily because of carotenoid pigments. 'Windsor Buttercup', for example, is a brilliant Yellow in terms of the Inter-Society Color Council—National Bureau of Standards (ISCC - NBS) Method of Designating Color. This is evident from instrumental color measurement; viz., 2.9Y 8.2/9.7 in Munsell notation.

In Munsell notation, color is defined in terms of Hue, Value, and Chroma. For the color of 'Windsor Buttercup', the first term (2.9Y) signifies a Yellow Hue, fairly close to a "middle" Yellow (5.0Y). The second term (8.2/) is Value (lightness) on a scale from 0 = Black to 10 = White. The third term (/9.7) is Chroma (a measure of color purity or saturation), which ranges from gray or white at very low levels up to 14 or 16 for vivid Yellow.

The only so-called "Yellow" evergreen azalea in my plant zoo is 'Olga Niblett'. The yellowish coloration found in evergreen azaleas results from the presence of flavonoid pigments such as aurones and xanthophylls that do not produce the high chroma found in deciduous azaleas (carotenoids may be present in the yellow spotting found on the upper petals of white corollas on some azaleas). In 1996 and 1999, my 'Olga Niblett' measured pale Yellow Green (ISCC - NBS) and visually was distinctly yellowish. This coloration is, however, variable (I shall not speculate on causes); in 2000, the chroma of 'Olga Niblett' was less than half of that measured in 1996, and the corresponding ISCC - NBS color name was yellowish White. As to visual evaluation of the color, "Yellow" would certainly have been an unwarranted stretch of accepted terminology.

Many evergreen azalea cultivars that are considered White have some Yellow or Yellow Green (or occasionally pinkish) coloration. As in the case of 'Olga Niblett', there may be year-to-year variation in chroma. As shown in the table, 'Papineau' in 1996 had Munsell Chroma = 0.9 (yellowish White); but in 2000, only 0.5 (White). Note that in bud or upon first opening, flowers of these plants often appear pale Yellow.

Several other "White" azaleas measured in 2000 are listed in the table. Each exhibits a high Value, and very low chroma. Their hues translate mostly to White or yellowish White in ISCC - NBS terms. Note, however, that in 'Treasure', in a "white" petal of 'Lady Robin', and in 'Mucronatum' the pigmentation is slightly redder and translates to pinkish White. (At slightly higher chroma, it would be pale yellowish Pink.) With the exception of 'Olga Niblett', all are considered to be "White."

Thus (at least for those unencumbered by measuring instruments, color charts, and ISCC-NBS terminology), Yellow, like beauty, is in the eye of the beholder!

Don Voss is a member of the Potomac Valley Chapter and Alternate District 9 Director.