The present invention relates to a solid color fade hydrogel cosmetic composition having flexibility through gamma ray irradiation. In a hydrogel cosmetic composition in an oil-in-water form comprising an aqueous phase part and an oil phase part, the aqueous phase part comprises 15 to 99.90 wt% of the total weight percent of the composition, the oil phase part comprises 0.10 to 85 wt% of the total weight percent of the composition, the refractive index difference between the aqueous phase part and the oil phase part is 0 to 0.02, and when applied to skin and irradiated with gamma rays, it is characterized by a color change caused by a change in the refractive index difference between the aqueous phase part and the oil phase part. The hydrogel cosmetic composition according to the present invention has flexibility through irradiation with gamma rays, and at the same time, when applied to the skin by using the difference in the refractive index between the aqueous phase part and the oil phase part in the composition, has the effect of visually confirming an optimal application time of the cosmetic composition through a color change from transparent to milky white by the change in the difference of the refractive index due to the degree of water absorbency and volatilization. In addition, the composition suppresses microbial growth of the cosmetic, thereby improving the quality of the product without adding a preservative that irritates the skin.La présente invention concerne une composition cosmétique d'hydrogel à décoloration de couleur solide, présentant une flexibilité par exposition aux rayonnements gammas. Dans une composition cosmétique d'hydrogel sous une forme huile-dans-eau comprenant une partie phase aqueuse et une partie phase huileuse, la partie phase aqueuse comprend de 15 à 99,90 % en poids du pourcentage en poids total de la composition, la partie phase huileuse comprend de 0,10 à 85 % en poids du pourcentage en poids total de la composition, la différe
