Master of Etherium's power and toughness are each equal to the number of artifacts you control.
Other artifact creatures you control get +1/+1.
The only difference between a colored artifact and a colorless artifact is, obviously, its color. Unlike most artifacts, a colored artifact requires colored mana to cast. Also unlike most artifacts, a colored artifact has a color in all zones. It will interact with cards that care about color. Other than that, a colored artifact behaves just like any other artifact. It will interact as normal with any card that cares about artifacts, such as Shatter or Arcbound Ravager.
The first ability works in all zones.
Since Master of Etherium is an artifact itself, while it’s on the battlefield you will usually control at least one artifact.