Before I buy another foundation I would like a steadier way to check my undertone. My phone photos look warm in the kitchen and cool beside the window. So I am planning to use indirect daylight and remove obvious color from the background. I am going to check simple white and gray references in the same light. Rather than calling the first result final I want to compare images made under nearly identical conditions. I found this skin undertone test camera keeps the experiment small enough to repeat. Once I have those notes I will try makeup samples on my jaw rather than my wrist. I would welcome advice from people who use phone photos about whether gray fabric is useful or just an unnecessary extra? 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.