From Beyond

An Eldrazi card is one with the creature type Eldrazi. Just having "Eldrazi" in its name or being an Eldrazi-themed card doesn't count.

Wotc — August 25, 2015

Cards with devoid use frames that are variations of the transparent frame traditionally used for Eldrazi. The top part of the card features some color over a background based on the texture of the hedrons that once imprisoned the Eldrazi. This coloration is intended to aid deckbuilding and game play.

Wotc — August 25, 2015

A card with devoid is just colorless. It's not colorless and the colors of mana in its mana cost.

Wotc — August 25, 2015

Other cards and abilities can give a card with devoid color. If that happens, it's just the new color, not that color and colorless.

Wotc — August 25, 2015

Devoid works in all zones, not just on the battlefield.

Wotc — August 25, 2015

If a card loses devoid, it will still be colorless. This is because effects that change an object's color (like the one created by devoid) are considered before the object loses devoid.

Wotc — August 25, 2015

Eldrazi Scions are similar to Eldrazi Spawn, seen in the Zendikar block. Note that Eldrazi Scions are 1/1, not 0/1.

Wotc — August 25, 2015

Eldrazi and Scion are each separate creature types. Anything that affects Eldrazi will affect these tokens, for example.

Wotc — August 25, 2015

Sacrificing an Eldrazi Scion creature token to add {C} is a mana ability. It doesn't use the stack and can't be responded to.

Wotc — August 25, 2015

Some instants and sorceries that create Eldrazi Scions require targets. If all targets for such a spell have become illegal by the time that spell tries to resolve, the spell won't resolve and none of its effects will happen. You won't get any Eldrazi Scions.

Wotc — August 25, 2015