Why is in Europe the date of spring start considered to be March 1, but in the America it falls on March 20 (21)?

We Americans, unlike the rest of the world, own Outer Space. So, we base the start of spring on the vernal equinox, which is on March 20th in the northern hemisphere. Other places, being ignorant of celestial goings-on, have decided to base the start of spring on the time when spring begins.

What color do you think the sky would be if we were in a different universe?

It would be smiznak, the color of molten tears from a nubala flemgoid.