[thangalin]

Here's XSLT code that transforms RGB colour space into LCH (and vice versa), which is then used to colourise an arbitrary number of visually distinct and harmonious pie chart wedges:

http://stackoverflow.com/a/25481023/59087

The algorithm is straightforward, albeit verbose.

[TeMPOraL]

I'll add my shot at converting RGB to CIE (XY + brightness) I wrote for my command line controller for Hue lights:

https://github.com/TeMPOraL/hju/blob/39b0c2c27f5f076a93b360d...

(code in Common Lisp)

Hue documentation (available after registering with them) also has example algorithm in (AFAIR) Objective-C.

EDIT: replaced Github link with commit permalink, in case I change the file in the future.