It works just fine on my Mac Pro running OS X 10.5.5. If it doesn't work on your machine there may be something wrong with Java on your system. The only way to know for sure would be to run another Java application and see how it works. You could also download and (re)install the latest Java update from Apple.

As a color picker, Colorspace is as good or better than the many alternatives out there. Whether it suits anyone's particular needs would depend on individual workflow requirements.