One-College Powerstone is a spell listed on the Spell Table on page 231 of GURPS Magic, separately from the Powerstone entry on M232.
It is not present in early errata from 2005 like [https://web.archive.org/web/20050205014953/http://www.sjgames.com/errata/gurps/4e/magic.html January 25] or February 25 but is present as of the October 23rd and subsequent 2006 editions.
- P. 70. One-College Powerstone should be a heading beneath the Powerstone spell. similar to those for Dedicated and Exclusive Powerstones - and not its own spell. Any mage who knows the Powerstone spell can enchant a one-college version for only 12 energy per point.
M69/M70 arranges it in this fashion in PDF version 1.0 (published 27 Feb 2006) implying it was presented differently in pre-1.0 versions. The PDF notes "All known errata as of the date of publication have been fixed." indicating that only physical copies of the book contained the OCPS spell as a standalone as implied by M231.
There don't appear to be special considerations for how this functions in respect to Limited Colleges Magery (like with Recover Energy) or Aspected Mana (not even Enchanting in Aspected Areas)
It's not clear if the original setup would've indicated a single spell titled "One-College Powerstone" or if it was intended to be multiple spells with the college title substituting, as with One-College Magery (ie "Fire Magery" and "Water Magery" = "Fire Powerstone" and "Water Powerstone").
There is not an equivalent One-College Manastone legally.