If i have an ability that protects my creatures against any color, how does that work with multi-color cards?

if i choose one of the colors of that card, am i protected against it or do i have to pick the color (golden) for the ability to work or are multi-color cards immune to protection from color abilities?

In MTG there are only five colors: White, Black, Green, Blue and Red. If a permanent has protection from any of them, then spells that has at least that color can't target the protected permanent.
For example, if you have a creature with protection from black (like white knight) you can not target it with mortify since mortify is black and white.
Altought multicolor cards have a golden border, gold is not a color in magic.
There are exceptions of course (like enemy of the guildpact), but most of the protection from color cards are pretty straightforward.

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