Magic: The Gathering has many mechanics with similar names that can make it difficult to determine exactly what some keywords do.
Intimidate, not to be confused with Menace or Fear, is a keyword ability introduced in the rulebook for Magic 2010, and the first cards printed with it came in Zendikar.
The mechanics of it are similar to Fear, which was widely known as a keyword exclusive to Black cards.
Intimidate is an “evasion ability” that makes it so a creature “can’t be blocked except by artifact creatures and/or creatures that share a color with it.”
If a creature’s color is changed during a turn, their color for the Intimidate mechanic will also change. But the colors involved in the Intimidate mechanic are only relevant up to the declaration of blockers. Once someone declares blockers, using an instant spell to change the color of a blocker will not change the status of that blocker.
Artifact creatures can block creatures with Intimidate even if they aren’t colorless. Their color plays no role in their ability to block.
Generally speaking, Intimidate is a lesser used keyword that has largely been replaced by Menace, which is a slight variation on evasion. Intimidate was last used in Magic 2015 and is considered a “deprecated” keyword, meaning it will likely not be printed again anytime soon due to balancing issues.
Overall, there are 38 cards that were printed with Intimidate and 60 percent of them were mono-Black. Another five percent were some variation of Black with either Green or Blue. The second most-used color for the mechanic was Red with just more than 18 percent of Intimidate cards having a Red mana symbol.