I built TEINT (teint.online), a free foundation shade finder for Filipino shoppers. It matches your skin tone from one selfie against 32 brands, 16 Filipino and 16 international, and runs right on your phone. I used Claude as my coding partner for the color science and face detection code. 1. Take or upload one selfie. 2. Face detection runs on your phone, so the photo is never uploaded. 3. The app corrects for the lighting, whether it is warm bulbs, daylight, or a dim room, before reading skin color. 4. It samples the skin tone in CIELAB color space. 5. It ranks shades from all 32 brands using CIEDE2000, a formula that measures how different two colors look to the human eye. 6. You get your closest matches in seconds. I also used Claude to generate shade guide pages for every brand so people can find the tool on Google. I wrote it in TypeScript and tested matches under different lighting before launch. The result is a short list of close foundation shades from a single photo, and the photo itself is never uploaded.