Selesnya Keyrune
Artifact
: Add 
or 
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: This artifact becomes a 3/3 green and white Wolf artifact creature until end of turn.
A mark of unity when you want one; a fierce guardian when you need one.
Daniel Ljunggren
The List (PLST)
• #RTR-233Rulings
Until the ability that turns the Keyrune into a creature resolves, the Keyrune is colorless.
(wotc • 2013-04-15)
Activating the ability that turns the Keyrune into a creature while it's already a creature will override any effects that set its power and/or toughness to another number, but effects that modify power and/or toughness without directly setting them will still apply.
(wotc • 2013-04-15)
Rulings
Until the ability that turns the Keyrune into a creature resolves, the Keyrune is colorless.
(wotc • 2013-04-15)
Activating the ability that turns the Keyrune into a creature while it's already a creature will override any effects that set its power and/or toughness to another number, but effects that modify power and/or toughness without directly setting them will still apply.
(wotc • 2013-04-15)