When you give a Kanban card a color, the whole card on the board now takes a light shade of that color, with a stronger edge. Before, only a thin strip on the left side showed it. Titles stay as easy to read as on a plain card, in light and dark themes.
Card colors shade the whole card
A Kanban card with a color now takes a light shade of it across the whole card, so colored cards stand out on the board.