This happens all the time. It even happens on earth! In simple terms, general relativity describes how gravity curves spacetime, which leads to length contraction and time dilation.

Special relativity describes a similar effect but for fast moving objects.

This effect can be measured for satellites in earth! GPS has to correct for the gravity difference AND the speed difference. The fast speed means time tick slower but the distance from earth gravity means the time tick faster. The total of the two effects is measurable and constantly being corrected. But for earth, the effect is small. Like microseconds small.

But other wise, yes, this is a very possible effect.

So that has been a misnomer for a while now. They used to use neon, which gives off the orange color but has since use other gases to produce the myriad of colors you see.

The blue comes from the gases in the environment. For lightning and other common sparks, it almost certainly happens in air. The combination of nitrogen and oxygen gives you the blue purple tint. BUT you can see a great example of different colored ‘sparks’ in neon lights! They fill the glass tubes with different gases to get different colors!