Not "flattering vs. unflattering" — "yours vs. not yours"
Colors don't have absolute value, but everyone has natural color characteristics that bias which hues look good close to the face. The same red coat is high-end on a Cool Winter and dated on a Warm Autumn.
Looksona doesn't tell you "don't wear this color because it's bad." It tells you which colors actually make your face come alive in photographs.
Three quick self-checks
1) Does this color make your skin look healthier (not yellow, not gray)? 2) Do your eyes look brighter against it? 3) Do you need fewer filters when you photograph in it? If yes to all three, the color suits you.
Looksona quantifies this — it uses your skin tone RGB and the target color's hue, brightness, and saturation to score how flattering the color is.