UK hospitals used to use plain white 100% cotton sheets, more recently they have changed to cotton and polyester also in plain white.
Generally vigoursly washed in very hot water, They last on average for about 100 cycles of use and laundering before becoming lost, stolen, ripped, damaged, or stained irrecoverably.

Patterned sheets are avoided for the reasons already given, but could be used in an emergency.

Hospital sheets are usually longer than those used in the home.