Spathiphyllum leaves are marked with golden yellow stripes and markings
This has been over the past 12 months or so, first a few leaves in a plant or two then in more and more plants, grown in almost full shade in self watering pots under a mango tree. My plants get fed seasol occasionally and I mostly use tank water on them.
Certified GKH Gardening Expert
Is it possible more sun is getting through than you know? Direct sun can cause streaking on peace lily leaves. If yours is dappled shade there could be direct sun getting through. Here is more information on the care of peace lilies.