[gwillen]

I noticed the author speculating about color, so I colorized it based on the identity of the largest prime:

http://jsfiddle.net/HEHHj/2/

It actually uses the last prime drawn, so it's only useful in 'smallest first' mode. That ought to be fixed, but I was lazy about it.

Colorizing the image based on the largest prime makes the pattern intelligible a little bit longer, before it becomes impossible to tell the big primes apart.