If the indicator is a 13, the okey wraps around and becomes the 1 of the same colour.

Normally the okey is one number above the indicator, but since 13 is the highest number, there is nothing higher, so it loops back to 1. For instance, a yellow 13 indicator makes the yellow 1 the okey joker for that hand. The two blank false-okey tiles would then stand in for the 13. This wrap-around rule keeps the joker system consistent no matter which tile is flipped as the indicator.