[metapost] MP docs : grey vs gray

[Nelson H. F. Beebe]

Dan Luecking <luecking at uark.edu> asks:

>> Why does MetaPost spell grey with an "e" (withgreyscale) while Postscript,
>> dvips and LaTeX all spell gray with an "a"?

Perhaps no one noticed before.

I use both spellings myself, as is common in English, and a google
search just now reports these frequencies on the Web:

	gray		140,000,000
	grey		120,000,000

	grayscale	  4,490,000
	greyscale	  1,430,000

	gray-scale	  4,640,000
	grey-scale	  1,510,000	

	color		521,000,000
	colour		123,000,000

Because of this confusion, software that uses them in keywords should
be prepared to handle either spelling (and both "color" and "colour").
PostScript does not, nor does gnuplot (it recognizes gray, but not
grey).

A check of my computer graphics books show that the 1979 SIGGRAPH CORE
proposal used "grey", but one GKS book, and Foley & Van Dam's book,
use "gray"; however, the word is absent from variable and routine
names, and from character-string arguments.  Tufte and White's books
use "gray" only.

John Warnock used "gray" in his important 1980 paper ``The display of
characters using gray level sample arrays'' that showed how to improve
the quality of font display.  Don Knuth used "gray" in his 1987 paper
``Digital Halftones by Dot Diffusion'', but "grey" appears in the
title of one of his references.

A search of the TeXbook source file, texman.tex, finds one use of
"grey" and zero of "gray", but in the METAFONT book source file,
mfman.tex, there are 38 uses of "gray", and 1 of "grey".  Neither word
appears in mf.web nor in tex.web.  

Curiously, "grey" appears 39 times in mp.web, and "gray" 3 times.

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