To activate the ability, you must sacrifice three different creatures. You can’t sacrifice just one three-colored creature, for example.

You may sacrifice the Herald itself to help pay for the cost of its ability.

You may sacrifice multicolored creatures as part of the cost of the search ability. If you sacrifice a multicolored creature this way, specify which part of the cost that creature is satisfying.

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.