Midvast Protector

Protection from the color of your choice is among the widest single-target answers white has, but here it is welded to development rather than held in reserve as a response. The entire effect lives inside the enters trigger, so the protection is tied to when the body arrives, not to a spell you hold up: deploy the creature, choose a color, point the grant at a threat already visible, and watch it fall off at end of turn. That timing is the whole shape of the card. On a plain hard cast this plays out on your own main phase, but the trigger is not intrinsically sorcery-speed; blink or flicker it in with another effect during an opponent's turn and the protection lands then instead, which is the one way to bend it into a reactive save. Absent that, you commit to the color in advance and cannot peel a creature off a targeted removal spell already on the stack. Remember what protection actually covers, though: it stops damage, blocking, targeting, and being enchanted or equipped by the named color, which means a color-matched damage sweeper like Blasphemous Act glances off, but a non-targeting destroy or -X/-X effect like Wrath of God or Toxic Deluge still kills through it. What the card does most reliably is proactive offense: push an attacker through a color-matched blocker, or grant temporary evasion the turn you need the damage to connect. The choose-a-color clause is what earns the 2/3 body, since a one-shot grant that can name any color covers far more ground than a fixed protection would. It belongs to white's long line of fair creatures that fold a small protective spell into their arrival.