[Objective] This study explored the effects of steaming/boiling time and cutting size on the color, texture, starch structure, and anthocyanin mass fraction of red and purple potatoes before and after cooking, aiming to provide a theoretical basis for the processing of colored mashed potatoes. [Method] Red and purple potatoes were taken as the research objects. They were cut into three different sizes (30 mm×30 mm×10 mm, 20 mm×20 mm×10 mm, and 16 mm×16 mm×10 mm) and steamed or boiled for five time periods (0, 3, 5, 7, and 10 min). The color parameters (including surface brightness L^*, red-green value a^*, and yellow-blue value b^*), texture properties (hardness, viscosity, chewiness, and adhesiveness), starch structure, and anthocyanin mass fraction were measured before and after steaming/boiling. The effects of steaming/boiling time and cutting size on the texture, starch gelatinization, and anthocyanin mass fraction of mashed potato were analyzed. [Result] Steaming/boiling time and cutting size had significant effects on the color, especially the L^*, a^*, and b^* values, of red and purple potatoes. With the extension of steaming/boiling time, the hardness, viscosity, chewiness, and adhesiveness of red and purple potatoes of all three cutting sizes showed a downward trend. Compared with steaming, boiling was more likely to cause the declines of these texture indicators. For potatoes with a cutting size of 30 mm×30 mm×10 mm, their texture indicators were significantly higher than those of smaller blocks (20 mm×20 mm×10 mm and 16 mm×16 mm×10 mm) under the same steaming/boiling time. For the blocks that could be made into mashed potato, steaming/boiling time and cutting size had greater impacts on the viscosity and chewiness of red mashed potato, but had no significant effect on those of purple mashed potato. Extending the steaming/boiling time to 10 min accelerated the starch gelatinization process, disrupted the starch structure, and caused a decrease in anthocyanin mass fraction. [Conclusion] The optimal processing conditions for colored potatoes are as follows: boiling for 7 min and cutting into blocks of 16 mm×16 mm×10 mm. The colored mashed potato prepared under these conditions has the best color and texture and can meet the quality requirements for the processing of colored mashed potato.