A.Myron Ferguson, a drywall contractor in Broadalbin, N.Y., and the author of Drywall: Professional Techniques for Walls and Ceilings, responds: Sunlight — as well as the mere passing of time — will cause the paper face of drywall to yellow or turn darker, a process that begins in less than a week if the drywall is exposed to direct sunlight (see photo).

The color typically bleeds through the compound when seams are taped, and it also bleeds through latex paint.

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