Ghostfire Blade
Artifact — Equipment
Equipped creature gets +2/+2.
Equip 
This Equipment's equip ability costs 
less to activate if it targets a colorless creature.
If you fear the dragon's fire, you are unworthy to wield it.
Cyril Van Der Haegen
Khans of Tarkir (KTK)
• #220Rulings
Face-down creatures and most artifact creatures are colorless.
(wotc • 2014-09-20)
Rulings
Face-down creatures and most artifact creatures are colorless.
(wotc • 2014-09-20)