The beautiful colors during rising or setting of the sun are caused by refraction of small water droplets or dust in the sky. A lot of humidity tend to make sky red and this color is dominant because it is the least refracted due to the longer wavelength in the spectrum of light.

The picture was taken at sunrise and shows cloudiness of an incoming frontal system moving eastwards. The ESE was still free of clouds hence the Altostratus opacus mamma was nicely sunlit.