Color Finesse isn't an additional purchase, it's installed automatically into After Effects by the Adobe CS4 and CS5 installers. In CS3 it was a separate installer on the Adobe DVD, but there was still a serial number for it included with AE. Look in the Effects menu under "Synthetic Aperture" and you should find Color Finesse.
Adobe does license it only for use in After Effects. If you want to also use it with Premiere Pro then you'd need to upgrade it through our web site to the "PI" version. Perhaps that's what you were thinking of. (If you think Adobe should also license it for Premiere Pro, let them know by filing a feature request.)
But for After Effects, Adobe has already paid for it for you, so please take advantage of that and get color correcting!
Bob Currier
Synthetic Aperture