Why d3 uses illuminant D50 instead of D65?

[michkowalczuk]

@mbostock ,
What is the reason that you decided to use illuminant D50 instead of D65 in d3?

CIE standard illuminant D65 values are:

Xn: 0.950470,
Yn: 1,
Zn: 1.088830

You use the following D50 values:

d3-color/src/lab.js

Lines 7 to 9 in 71c7f10

	Xn = 0.96422,
	Yn = 1,
	Zn = 0.82521,

For example chrome.js uses D65:
https://github.com/gka/chroma.js/blob/cd1b3c0926c7a85cbdc3b1453b3a94006de91a92/src/io/lab/lab-constants.js#L6-L9

[danburzo]

D50 is the illuminant used in CSS for lab() / lch() colors, as well as in graphics applications such as Adobe Photoshop. See also: gka/chroma.js#278