Phosphoric acids used in metal cleaning solvents and etchants can, if left on and not thoroughly washed off, cause a fast growing surface bloom of yellow FeO2. But, I don't see how you could color case harden or blue with solvents left on the metal surface.
Yes, annealing alters surface molecular structure, I assume by spacing the surface molecules further apart. It has to, because the surface is softer, but I don't know how.
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