A common mistake I see newer (and some veteran!) players making is misunderstanding how a permanent’s colors work. For example, I’ve seen many a person think that when Doom Blade says it destroys a nonblack creature, what that means is that the creature has to be a color that isn’t black. So, by their logic, an Exava, Rakdos Blood Witch is a nonblack creature in terms of whether or not they can [card]Doom Blade it, because she’s red! Red is nonblack, right?

The problem with that line of thinking is… well, it’s wrong. When something in Magic refers to a characteristic like color (or in the case of Doom Blade, the lack of that characteristic), it’s only asking about that, nothing else. “Nonblack” does not mean “White, blue, red, green, or colorless”, it means “not at all black”. If the answer to the question “is that creature black?” would be yes, then the creature is black. Doesn’t matter if the creature is also white, blue, green, or red, all this spell cares about is whether the creature is black or not. Compare that to Farseek; it says to search for an Island, Swamp, Plains, or Mountain. While Forest isn’t listed, it doesn’t say “Search for a non-Forest land”, because you can find a Breeding Pool or a Temple Garden or a Bayou with Farseek, because it fits the criteria of ‘one of these four types’. This is the OPPOSITE of Doom Blade, which only cares that the creature isn’t black, rather than it being another non-black color.