In addition to white towels for showering, etc, you will be provided with pool towels in your stateroom, which will be replaced by your stateroom steward when necessary. Enjoy your cruise on Sea Princess, she is a lovely ship.
I also thought that there were towels near the pool - I think that they were blue and you use and leave them in another basket near the pool.
There are supplied white towels for use in your cabin but also blue/white stripe ones for the pool
We (and just about everyone else) also took the B/W stripe ones on beach / snorkelling excursions