In Visual Interface (VI) design, choosing auxiliary colors to complement the primary blue color is essential for creating a harmonious and visually appealing interface. Auxiliary colors are secondary colors used to enhance contrast, highlight important elements, and create a balanced color scheme. Common complementary colors to blue include orange, yellow-green, and purple. These colors can be used in varying intensities and shades to achieve the desired visual effect. When selecting auxiliary colors, it's important to consider the color theory principles of contrast, harmony, and contrast to ensure the interface is user-friendly and aesthetically pleasing.