Step 1: Identify the defining characteristic described in the question: a gradual color transition, resulting in a hazy effect.
Step 2: Assess the provided options.
Realism: Represents subjects accurately, without artificiality; it is a style, not a blending technique.
Foreshortening: Creates the illusion of depth by depicting an object receding into the distance.
Husconism: An unrecognized term in art.
Sfumato: (Italian for "to tone down" or "to evaporate like smoke") Specifically softens color transitions, producing a soft, hazy appearance. Leonardo da Vinci is a prominent practitioner.
Therefore, Sfumato is the correct choice.