I have a house plant and the leaves are getting lighter. I believe the name of the plant is a Silver Queen or Silver king.
I have had this plant for about a year. watered when needed like I always have. And I have never seen this.
I bet you have a Silver Queen aglaonema.
Couldn't tell you why the leaves are lightening up, but you'll get more attention to your question if you post it over in the "Discussions" area of the houseplants forum....this is more the area for off-topic stuff.
Sorry I couldn't be more help