Finding the perfect foundation shade can be tricky when you can't try it on in person. However, there are a few ways to determine your ideal shade. First, you need to identify your skin's undertone, which can be cool, warm, or neutral. Then, you need to choose foundation shades that match your undertone and your skin color. You can test the shades on your jawline or cheeks to see which one blends seamlessly into your skin. You may need to use more than one shade to highlight different areas of your face. There are also online tools that can help you find your perfect foundation shade by inputting your current shade of foundation and finding its matching shade in another brand/formula.