$.fn.colorbox Vs. $.colorbox

So I'm, trying to use Splash with colorbox on a D6 site here and am having a bit of trouble. Playing around with the code, it seems that the js included to add a colorbox uses the prototype alias syntax call $.fn.colorbox(), which seems like it should be perfectly valid, but this does not work. However, calling as $.colorbox() does and this is also how I see it typically used. I'm not very familiar with the internal workings of the colorbox library, but it seems that it is interpreting the prior as an empty collection. Am I just missing a step in the configuration here?