Random Riddle: I Am I

When of wind I am the calm
The center holding still.
When of you, a different part
My bottom lid, my sill.

You may look into me
only to see through.
You may indeed look out of me
Through my frame of varied hue.

The riddle in three parts
as letters in my name.
The riddle shows you who I am
But tell me just the same.

Who am I?