Protection works via the DEBT acronym: the protected permanent cannot be Damaged, Enchanted/Equipped/Fortified, Blocked, or Targeted by anything that matches the protection's quality (CR 702.16b). A gold card — one with two or more colors — is a multicolored source, so protection from multicolored applies fully against it.
This means a creature with protection from multicolored cannot be targeted by abilities of a multicolored card. If a multicolored spell or activated/triggered ability from a multicolored permanent tries to target the protected creature, that target is illegal and the spell or ability cannot be cast or activated targeting it in the first place (CR 508.1c, 601.2c).
It also means a multicolored creature cannot deal combat damage to the protected creature, cannot block it, and multicolored Auras or Equipment cannot be attached to it. All four prongs of DEBT apply to the multicolored source regardless of whether it is a spell, permanent, or ability (CR 702.16b, 702.16e).
Example: Your opponent controls Sovereign's Bite as part of a multicolored instant. Your creature has protection from multicolored. Your opponent cannot target your creature with that spell. If somehow it were on the stack already targeting the creature (e.g., the creature gained protection in response), the spell's effect is prevented entirely when it tries to resolve — the creature is an illegal target and the spell is countered on resolution (CR 608.2b).
Note: Protection only covers abilities that originate from a multicolored source. If a multicolored permanent has an ability that creates a colorless or mono-colored effect, the source still matters — the ability's source is the multicolored card, so the protection applies (CR 702.16e).
Unofficial fan resource — not affiliated with or endorsed by Wizards of the Coast. Answers are AI-generated estimates grounded in the Comprehensive Rules and are not a substitute for an official judge. Verify anything match-critical.