Shifting Sky

As Shifting Sky enters, choose a color.
All nonland permanents are the chosen color.

Nantuko Blightcutter

Protection from black
Threshold — Nantuko Blightcutter gets +1/+1 for each black permanent your opponents control as long as seven or more cards are in your graveyard.

Painter's Servant

As Painter's Servant enters, choose a color.
All cards that aren't on the battlefield, spells, and permanents are the chosen color in addition to their other colors.

Aragorn, the Uniter

Whenever you cast a white spell, create a 1/1 white Human Soldier creature token.
Whenever you cast a blue spell, scry 2.
Whenever you cast a red spell, Aragorn, the Uniter deals 3 damage to target opponent.
Whenever you cast a green spell, target creature gets +4/+4 until end of turn.