fshanno said:
1/2" Maple ply, book matched veneer. One half is much lighter after stain. Shellac and sealers applied before stain make it worse. Both sides look fine but one is much lighter.
It's reflectance. It's because it's book matched. Walk around to the opposite end and the light/dark pair will flip.
The grain is going in opposite directions between one half of a book matched pair and the other half. When the grain is fairly parallel to the panel surface the effect is more subtle and usually the strips that make a book matched pair are narrow enough that in the worst case the effect makes the panel look subtley striped rather than one half is wrong.