Fig. 1

Schematic cross section of hair"

Fig. 2

（A） Monomer structural formula of melanin; （B） the synthetic pathway of melanin"

Fig. 3

Three most common signaling pathways for regulating melanin synthesis"

Fig. 4

Effects of mangosteen pericarp extract at different mass concentrations on the melanin of dermal papilla cells"

Fig. 5

The melanin content of HMVII melanoma cell line after treatment with sterubin （A）; cellular immunohistochemistry after exposure to sterubin （B）; after treatment with sterubin, the expression of β-catenin, MITF and TYR （C, D, E）"

Fig. 6

The melanin content and the quantity of cells treated with different samples （A）; concentration dependence of the effects of 4′-O-methyl-type flavonoids on the melanin content in B16F10 melanoma cells （B）; effects of flavonoids on tyrosinase activity （C）"

Fig. 7

Effects of kaempferide and isorhamnetin on melanin in adult zebrafish depigmentation model （A）; effects of kaempferide and isorhamnetin on the levels of MC1R and MITF mRNA in zebrafish larvae （B, C）"

Fig. 8

Compared with commercial permanent black hair dye, the hair-dyeing effect of graphene with increasing concentration （A）; SEM images of uncoated and coated hair （0.25%） （B）; the glossiness of uncoated and graphene-coated hairs, and those treated with the commercial permanent black hair dye （C）; representative stress-strain curves of a strand of hair before and after graphene coating （D）"

Fig. 9

Photos （A） and ΔE values （B） of hair samples. ① Virgin gray hair and PDA-dyed hair samples dyed in different conditions; ② Cu2++H2O2; ③ Cu2++H2O2′; ④ Tris; ⑤ Tris′; ⑥ NaIO4; ⑦ NaIO4′; ⑧ Commercial dye. “′” represents the samples that underwent a pregrafting treatment"

Fig. 10

Photos of dyed hair samples after washing. Samples from right to left are hair dyed with PDA without pregrafting, PDA with pregrafting and commercial dye"