Your devotion to two colors is the number of mana symbols among mana costs of permanents you control that are the first color, the second, or both. If an effect counts your devotion to two colors, a hybrid symbol that is both of those colors is counted just once.

March of the Canonized's last ability will trigger only if your devotion to white and black is seven or greater at the beginning of your upkeep. As the triggered ability tries to resolve, if your devotion to white and black is no longer at least seven, the ability won't do anything.

Colorless and generic mana symbols ({C}, {0}, {1}, {2}, {X}, and so on) in mana costs of permanents you control don't count toward your devotion to any color.

Mana symbols in the text boxes of permanents you control don't count toward your devotion to any color.

Hybrid mana symbols, monocolored hybrid mana symbols, and Phyrexian mana symbols do count toward your devotion to their color(s).

If you put an Aura on an opponent's permanent, you still control the Aura, and mana symbols in its mana cost count toward your devotion.

The back face of a transforming double-faced permanent has no mana cost. Mana symbols on a transforming double-faced permanent's front face don't count toward your devotion to any color while it's on the battlefield with its back face up.