“Again, though these answers are correct, the deeper explanations are yet more interesting, and even simpler…

1) Sky is blue – thinness of the atmosphere allows only the very highest energy wavelengths to be scattered, while the lower energy wavelengths can endure the transit through the atmosphere to our eyes. Evenings and mornings are colored, as the light must travel a longer distance through the absorbing atmosphere – and thus lower and lower wavelengths get scattered.

2) Grass is green because it absorbs other wavelenghts, but interestingly it is tuned evolutionarily to be as maximally efficient in absorbing light from our sun as possible. The green color comes as a side effect of absorbing the most highly energetic light coming from the sun. Change the energetic maximum from the sun, and plants colors would change to match it.

3) The highest energy light coming from the sun (that the green plants absorb) is directly related to the emission from the particular elements that make up the sun. Dependent upon the size and composition of the sun (percent Hydrogen, helium, etc.) the emission spectra will be of a particular color.

These three are all tied to basic physical processes. The sun emits its color from electrons jumping from very particular heights based on the elements in the sun. The sky is the color it is because of how the atmosphere absorbs the sun’s emissions. And the plants are the color they are in order to maximize energy absorption of the sun’s light that reaches them through our atmosphere.”

See:
http://www.reddit.com/r/science/comments/8vz3u/why_the_sky_is_blue_the_grass_green_the_sun_yellow/