Boros Keyrune
Artifact
: Add 
or 
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: This artifact becomes a 1/1 red and white Soldier artifact creature with double strike until end of turn. (It deals both first-strike and regular combat damage.)
Daniel Ljunggren
Gatecrash (GTC)
• #227Rulings
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)