Question

Why do we observe difference in colours of the sun during sunriseand noon?

Answer 1

during sunrise, the part of the earth you are in emerges from the darkness into the light rays of the sun thereby facing the sun rays while at noon, that part of the earth moves way from the sun due to rotation of the earth thereby backing the sun rays

Answer 2

Sun appears red at sunrise and sunset : At sinrise and sunset, sun is closer to the horizon. The sunlight passes through denser layer of air and covers larger distance before reaching our eyes. Most of the blue light gets scattered. The light that reaches our red. That is why the sun appears red at sunrise. 

At noon, the sun is overhead. The sunlight passes through rares layers of air and covers shorter distance before reaching our eye. So, almost all colours of light are scattered equally. Hence the sun appears white