What color will the sky be?

For those who have travelled to high country, have you ever noticed
that the sky is a deeper blue?

I think that this is because there is less water vapor and a lower
atmospheric density at those altitudes so the blue light gets
scattered less, resulting in a deeper blue.

Is this correct?

If so, and let's say we're in an Island 3 with 1/2 atm, wouldn't we
expect the sky to be almost a dark/royal blue, rather than the sky
or light blue that most of us are used to?

Doesn't liquid oxygen have a blueish color to it?

If the atmosphere is 50% O2 and 50% N2, would that change the color
of the sky?

TangoMan