It can be analyzed in this way.
1. Because your friend is thin and has dark yellow skin, you should wear as little dark clothes as possible, such as gray, green, cyan, dark blue, purple, yellow and gray, because wearing dark clothes will look haggard and listless. Black is dark, so don't choose a black dress, not to mention the visual effect of slimming and shaping.
2. White, light blue, beige and other light colors are more suitable for her, which can make her look less thin visually, and the color tone is also in line with her dress. I have been making clothes for more than ten years, I can guarantee this.
3. It would be better if it is red or red striped red plaid clothes. You can trim your face and look better.