Colours near the red end of the spectrum scatter the least. This happens because of short wavelength of reddish colours. During sunset and sunrise, sunlight needs to travel more distance to reach us. Red colour is able to reach us because it is scattered the least. Hence, sky appears reddish during sunrise/sunset.
 The sky appears reddish during sunrise/sunset but it appears white at noon. During noon, the sunlight has to travel less distance to reach us. Most of the colours reaching us get scattered. Due to this, sky appears white at noon

When ray of light enters a prism, it bends because of refraction of light. When the ray of light finally emerges out of the prism, it deviates drastically from its original path. This happens because of unique shape of prism. Different colours in the visible spectrum have different speeds. Due to this, different colours bend at different angles of deviation. As a result, the emergent light appears as a band of seven colours; the colours which are the components of white light. These colours are Violet, Indigo, Blue, Green, Yellow, Orange and Red. Segregation of white light into its different components is called dispersion of light. 

Atmosphere is made up of several layers. The layer at the top is optically rare, while the layer at the bottom is optically denser. Due to this, when light travels through different layers of the atmosphere, refraction takes place. Since light passes through denser and denser layer as it moves through atmosphere, it tends to bend towards the normal. Stars are very far from us; compared to planet. Due to this, stars serve as point source of light. As a result, even a slightest change in their apparent position in the sky is clearly perceived by us. Hence, stars appear to twinkle. Planets on the other hand, are near to us. Hence, they do not serve as point source of light. Hence, minor changes in their apparent position are not perceived by us. Hence, planets do not appear to twinkle.