Single-shade and simplified-shade resin composites are designed to simplify clinical application through enhanced color adjustment potential. However, compositional modifications used to simplify shade selection may affect the physicochemical and mechanical properties of these composites, especially during extended water exposure, which occurs in the oral cavity. This study aimed to evaluate the degree of conversion, water sorption, solubility, and microhardness of two single-shade composites (Omnichroma and Essentia Universal), one simplified-shade composite (Tetric Plus), and a conventional composite (Tetric Prime) as a reference material. Disk-shaped specimens (d = 6 mm, h = 2 mm) were stored in distilled water at 37 °C for 3 months to evaluate water sorption and solubility. Vickers microhardness was measured before and after 3 months of water immersion. Degree of conversion was evaluated immediately and after 1 and 3 days. The single-shade composite Omnichroma exhibited the highest degree of conversion, but also the highest water sorption (21.7 μg/mm³), and was the only material that showed a positive solubility value (2.9 μg/mm³). In contrast, the reference composite showed the highest microhardness (51.8–60.2 VH). Omnichroma and Tetric Plus demonstrated lower microhardness than the reference material, whereas Essentia Universal showed significantly lower microhardness (38.4–42.1 VH) despite nominally high filler content. These findings indicate that degree of conversion, water sorption, solubility, and microhardness differed among the tested products and appeared to depend on their specific composition rather than on the color-adjustment concept alone.