They CAN shrink from the heat of the washing machine and definately in the dishwasher.
I have the very light (pearl?) grey and frankly I have not been able to keep them clean. I wash them in the washing machine on cold weekly and have tried scrubbing with soap and water, and have tried a magic eraser. I did let her play in the pool wearing them and that helped quite a bit but now that the pool is closed for the season it has been a loosing battle.
Honestly, those of you that keep them clean, are they the very light colored ones?