See:

http://www.ledet.com/margulis/2010HTM/ACT08-Jacobs_Ladder.htm

http://www.hcs.harvard.edu/~jrus/colortheory/jl.html

http://www.curvemeister.com/forum/index.php?board=58.0

http://www.broadhurst-family.co.uk/lefteye/MainPages/jacobsladder.htm