A.Michael Dresdner, a professional wood finisher in Puyallup, Wash., and the author of Wood Finishing Fixes, responds: Depending on what the painter used to bleach the wood, it's possible that residue from the bleach reacted with the stain. Most bleaches will denature dyes, and some brands of stain use dye as one of their colorants. Because bleach affects various colors of dye at different rates, it may well have lightened some of the darker tones and left the yellow component intact, resulting in the yellow hue you describe. When you use bleach, it is always a good idea to either neutralize it or wash off any residue if that particular bleach leaves one.
Another possibility is that the wood itself turned yellow, which, since it is so difficult to see true colors on sanded raw wood, the painter didn't notice until it was stained. Certain bleaches are known to lighten most woods while turning others — especially some softwoods — slightly yellow.
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