Corrupted Shapeshifter

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

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.

Devoid doesn't affect the color identity of the card for the purposes of the Commander variant. For example, while Abstruse Appropriation is colorless because it has devoid, its color identity is still white and black, and it can't be included in a Commander deck where the commander's color identity doesn't include both white and black.

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

If a permanent enters the battlefield as a copy of Corrupted Shapeshifter, there will be two copy effects to apply to it. One will copy the values chosen for the Corrupted Shapeshifter being copied. And you'll choose the values for the copy's own enters-the-battlefield replacement effect. The resulting permanent will have the abilities from both effects, and its power and toughness will be determined by the last effect to apply. For example, if a creature entering the battlefield is copying an 0/12 Corrupted Shapeshifter with defender, you could make it a 3/3 or an 0/12, either way with flying and defender.

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