The extended duration at residual temperature could indeed contribute to an ash-colored appearance of the material, depending on the material’s composition, the temperature range, and the environmental conditions during exposure. Residual temperature, often referring to elevated temperatures maintained after a primary heating process (e.g., in combustion, pyrolysis, or thermal processing), can drive chemical and physical changes that alter a material’s color. For organic materials, prolonged exposure to even moderate residual heat (e.g., 200–400°C) can cause thermal degradation, charring, or carbonization, leading to a gray or ash-like appearance due to the formation of carbon-rich residues or partial oxidation of organic components. For inorganic materials, such as metals or ceramics, extended time at residual temperatures may induce surface oxidation, phase changes, or sintering, which can produce a dull, grayish, or ashen hue, as seen in oxidized iron forming grayish iron oxides. The presence of oxygen, moisture, or other reactive species in the environment can exacerbate these effects, promoting reactions like oxidation or the formation of colored byproducts. For example, in biomass pyrolysis, extended exposure to residual heat in an oxygen-limited environment can yield ash-colored char due to incomplete combustion. The specific temperature, duration, and material composition are critical; longer durations at lower temperatures can sometimes cause more pronounced color changes than short, high-temperature exposures due to cumulative chemical changes. If you provide details about the material, temperature, and process (e.g., combustion, annealing), I can refine the explanation. Would you like me to search for studies or posts on this topic to provide further context?