Diamond Knight 
Artifact Creature — Knight
Vigilance (Attacking doesn't cause this creature to tap.) As this creature enters, choose a color. Whenever you cast a spell of the chosen color, put a +1/+1 counter on this creature.
Legality
standardNOT LEGALpioneerLEGALmodernLEGALlegacyLEGALvintageLEGALcommanderLEGAL