Two effects that both contribute to the reason for seeing "blue not violet":
1. The sun puts out light that has more blue light in it than violet. The solar spectrum peaks in yellow - you can see that with this illustration: http://en.wikipedia.org/wiki/File:Solar_Spectrum.png
This is why the sun looks yellow to us. Violet is further from yellow than is blue, and hence there is less violet light than blue light in the sun's spectrum.
2. Human eyes have evolved to see in a wavelenth band centered on yellow (as that's where the most light is), and so our eyes are less adept at seeing violet light than blue. Hence we perceive light that has both blue and violet in it as being basically blue.
These effects combine so that blue swamps out violet in the way we perceive the color of the sky.
The sky color from our earth is green and on mars its red, because of the environment of planets, on earth there are so much gases where oxygen and hydrogen are in majority that is why sky looks green from here.
Actually nitrogen is the majority of gas in the earth's atmosphere, followed by oxygen. Hydrogen is present only in very small concentration - only about 0.000055%. But even if you were right about the composition of the atmosphere, it would not explain why the sky is blue. You really must consider the scattering of sunlight to explain it.