<p>Monolithic zirconia has become increasingly popular in prosthodontics due to its favorable mechanical and esthetic properties. However, exposure to acidic conditions, such as simulated gastric acid, may compromise its optical and surface characteristics. This in vitro study aimed to evaluate the effects of three different surface modification technique mechanical polishing, polishing followed by glaze application, and polishing followed by zirconia–silica coating on the color stability and surface roughness of monolithic zirconia under acidic and neutral conditions. Forty-eight monolithic zirconia specimens were randomly assigned to six groups according to the surface modification technique and immersion medium (distilled water or simulated gastric acid). Color differences (Δ<i>E</i>₀₀) were calculated using the CIEDE2000 formula, and surface roughness was assessed using Atomic Force Microscopy (AFM). Data were analyzed using two-way ANOVA and Tukey’s HSD post hoc test (<i>α</i> = 0.05). Surface modification technique significantly affected Δ<i>E</i>₀₀ values (<i>p</i> = 0.00015), whereas neither the immersion medium nor the interaction between the two factors was statistically significant. The mechanically polished group exhibited the highest color change. Regarding surface roughness, exposure to acidic conditions resulted in smoother surfaces in the mechanically polished and polished + glaze groups, whereas an increase in roughness was observed in the zirconia–silica-coated group. Surface modification techniques play a critical role in the esthetic and structural integrity of monolithic zirconia restorations. Glazing and zirconia–silica coating improved color stability and maintained surface characteristics more effectively than mechanical polishing alone. The influence of solution pH was minimal. These findings support the use of appropriate finishing techniques to enhance the clinical longevity of zirconia restorations.</p>