Aphotic Wisps — ruling 1

An effect that changes a permanent’s colors overwrites all its old colors unless it specifically says “in addition to its other colors.” For example, after Cerulean Wisps resolves, the affected creature will just be blue. It doesn’t matter what colors it used to be (even if, for example, it used to be blue and black).

Aphotic Wisps — ruling 2

Changing a permanent’s color won’t change its text. If you turn Wilt-Leaf Liege blue, it will still affect green creatures and white creatures.

Aphotic Wisps : règles, fonctionnement et interactions (MTG)

Aphotic Wisps is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Target creature becomes black and gains fear until end of turn. (It can't be blocked except by artifact creatures and/or black creatures.) Draw a card.

How it works : Aphotic Wisps

Original English text — Wizards of the Coast / Scryfall

#1May 1, 2008· Wizards of the Coast
An effect that changes a permanent’s colors overwrites all its old colors unless it specifically says “in addition to its other colors.” For example, after Cerulean Wisps resolves, the affected creature will just be blue. It doesn’t matter what colors it used to be (even if, for example, it used to be blue and black).
No other card is named in this ruling.
#2May 1, 2008· Wizards of the Coast
Changing a permanent’s color won’t change its text. If you turn Wilt-Leaf Liege blue, it will still affect green creatures and white creatures.
No other card is named in this ruling.
#3May 1, 2008· Wizards of the Coast
Colorless is not a color.
No other card is named in this ruling.