A solid temporal colorimetric hydrogel cosmetic composition includes 15 to 99.90 wt % of the water phase part and 0.10 to 85 wt % of the oil phase part, having a refractive index difference of 0 to 0.02 therebetween, and having a color change according to variations in a refractive index difference between the water phase part and the oil phase difference when applied to the skin. The cosmetic composition not only has flexibility through irradiation of gamma-rays, but also enables an optimal application time of the cosmetic composition to be visually confirmed through a color change from transparency to ivory white due to a change in the refractive index difference caused by absorbency and volatilization of water when applying the composition to the skin. The cosmetic composition is capable of improving quality of a product although a preservative irritating to the skin is not added.