Blue ink, food, pigments and dyes, and traditional seals all print blue things on your fingers.

1, blue ink: When using some stationery such as pens and signature pens, blue ink handprints will be left on your fingers.

2, food: some foods such as blueberries, blackberries, seaweed and so on. After eating, you will leave a blue mark on your finger.

3. Paints and dyes: Blue paints and dyes will be applied to fingers, and if they are not completely dried, they will leave blue marks.

4. Traditional seal: the traditional seal uses blue ink, and the fingers are easily contaminated with blue ink when stamping.