Sway of Illusion

Any number of target creatures become the color of your choice until end of turn.
Draw a card.

Insight

Whenever an opponent casts a green spell, you draw a card.

Invoke Prejudice

Whenever an opponent casts a creature spell that doesn't share a color with a creature you control, counter that spell unless that player pays {X}, where X is its mana value.

Scuttlemutt

{T}: Add one mana of any color.
{T}: Target creature becomes the color or colors of your choice until end of turn.

Distorting Lens

{T}: Target permanent becomes the color of your choice until end of turn.

Mana Maze

Players can't cast spells that share a color with the spell most recently cast this turn.

Blind Seer

{1}{U}: Target spell or permanent becomes the color of your choice until end of turn.

Dismiss into Dream

Each creature your opponents control is an Illusion in addition to its other types and has "When this creature becomes the target of a spell or ability, sacrifice it."

Llawan, Cephalid Empress

When Llawan, Cephalid Empress enters, return all blue creatures your opponents control to their owners' hands.
Your opponents can't cast blue creature spells.

Essence Leak

Enchant permanent
As long as enchanted permanent is red or green, it has "At the beginning of your upkeep, sacrifice this permanent unless you pay its mana cost."

Chameleon Spirit

As Chameleon Spirit enters, choose a color.
Chameleon Spirit's power and toughness are each equal to the number of permanents of the chosen color your opponents control.

Tidal Visionary

{T}: Target creature becomes the color of your choice until end of turn.

Heartstone

Activated abilities of creatures cost {1} less to activate. This effect can't reduce the mana in that cost to less than one mana.