Comparing deep and soft palettes in daylight

Before ordering foundation I am trying to understand my undertone more carefully. I notice that phone images can appear inconsistent whenever I change rooms. So I am planning to stand near a window with indirect natural light. I am going to check white paper and soft gray fabric beside my face. Rather than calling the first result final I plan to look for patterns across several similar photos. A short skin undertone test camera seems helpful because it separates lighting notes from color observations. With a few consistent images I can look at foundation samples without changing the lighting again. If this method sounds familiar, could you say whether which simple step matters most before comparing undertones? I know a camera cannot replace seeing real skin in changing light, and I am not expecting a perfect answer from one home experiment. My goal is simply to make the next store visit less confusing. Keeping a short record of conditions should also help me recognize when a surprising result is probably caused by lighting rather than my actual coloring.