Question about checking an undertone at home

I am looking for a practical way to photograph skin tone under stable light. I have noticed that automatic settings can hide the differences I am looking for. I want to begin in even daylight instead of mixing several light sources. I intend to leave off filters, flash, portrait mode, and beauty adjustments. A small grey reference seems more dependable than judging one image in isolation. My goal is to retake the same photos on a second day for comparison. A well-organised skin undertone test camera might be a useful checklist before I compare the photographs side by side. I understand that screen calibration and seasonal light still limit this kind of exercise. Looking at matched photos together should reveal whether the change is actually consistent. Have you found a reliable setting that reduces dramatic colour shifts? I am hoping to keep the process accessible and repeatable. I will avoid changing the setup halfway through the small experiment. Thank you for sharing any small details that made your comparison clearer.