Hours of work went into this, and unintentionally it turned out as a pretty spiral graph creator. The colours are a bit washed and green, I was experimenting with fading pixels together.
I ended up having to use code by Jared Tarbel to fade the pixels together. Apparently set() pixel in processing doesn't overlay transparency.
I found a brilliant resource for curves at //www.xahlee.org/SpecialPlaneCurves_dir/Intro_dir/familyIndex.html
which contains all the useful Math and pretty pictures for building your own.
The original aim was infact to build (on my own) a pretty particle generator, similar to ones by Jared Tarbel and also as seen at //www.processing.org
The type of curve being drawn is actually called a 'Rose'. I recgonised it from my old spiralgraph set which I had when I was kid (it used cogs with holes which you ran round a sheet of paper to draw pretty patterns).
Mmm, this processing lark seems pretty fun.