Jose writes:

Not cyan. Rather, class E is depicted by that horrible purply color the
FAA erroniously calls "magenta". What they print on the chart is not
magenta by any stretch of the imagination. Magenta is beautiful; you
can see magenta in the deluxe Crayola crayon box. The FAA color should
be called "FAA feh".

Cyan is more like a deep blue. Real cyan is also beautiful.

Cyan is an equal blend of green and blue. It is used in process
printing as one of the four base colors. Magenta is another one of
those colors, and it is an equal blend of red and blue. The other two
colors are yellow and black. By blending these colors in various
proportions, you can produce virtually any color of the rainbow on
paper.

I'm not sure why the FAA chose these colors, but one possible reason
is that they blend easily when they overlay other colors, which
probably makes it easier to produce semitransparent borders with them.
You can get away with simply overprinting cyan and magenta halftones;
doing the same with primaries like red or blue (which are already
screened blends) might just get you a muddy black.

With modern electronic illustration and mapmaking this could probably
be changed, but it looks like aviation charts are still being drawn
and modified by hand--they lack the crisp look of something original
prepared on a computer. It must be hugely labor-intensive.

--
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