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.

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.

Ulalek must be on the battlefield in order for its triggered ability to trigger. Casting Ulalek itself won't cause that ability to trigger.

Each copy will have the same targets as the spell or ability it's copying unless you choose new ones. You may change any number of the targets, including all of them or none of them. If the spell is a permanent spell with targets, such as an Aura, you may also choose a new target for that spell. The new targets must be legal. If, for any target, you can't choose a new legal target, then it remains unchanged (even if the current target is illegal).

The copies are created on the stack, so they're not "cast" or "activated." Creating the copies won't cause abilities that trigger when a player casts a spell or activates an ability to trigger. Abilities of copied spells that say "When you cast [this spell]" won't trigger.

If the spell or ability that's copied is modal (that is, it says "Choose one —" or the like), the copy will have the same mode or modes. You can't choose different ones.

If the spell or ability that's copied has an X whose value was determined as it was cast or activated, the copy will have the same value of X.

If the spell or ability that's copied has damage divided as it was cast or activated, the division can't be changed (although the targets receiving that damage still can). The same is true of spells and abilities that distribute counters.

The controller of a copy can't choose to pay any alternative or additional costs for the copy. However, effects based on any alternative or additional costs that were paid for the original spell are copied as though those same costs were paid for the copy.

Resolving copies of permanent spells become tokens as they enter the battlefield. These tokens are not considered "created" when this happens.

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

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.