What am I? #4

I can appear to sweep and sway in a varied motion.
Mystery and wonder always seem to follow me.
I can appear gray to some and blue to others.
I can roll although I am not solid.
Only from a distance can I be viewed.
However you may chase me, I am always just a bit ahead.
Swamps and other humid places are what I normally call home.
What am I?

Highlight for the answer.
Answer: [ Fog/Mist ]

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