iOS popup close button label OK or Okay

Question

I'm working on an iPhone app with custom popup alerts. In the design these alerts all have "Cancel" buttons, but since there is nothing to cancel in these cases, I want to change them to "Okay" buttons.

My question is this: What are the Apple guidelines regarding these button labels? Should it be "Okay" (which is my personal preference), or should it be "OK" (which I don't like because it looks like teen-text-speak or the state abbreviation for Oklahoma).