Joico Colour Balance Blue Conditioner is a blue-toning conditioner made for lightened or highlighted brunette hair — it targets the orange and brassy tones that show up as brown hair is lifted, using blue pigment to cancel them out on the color wheel. This is the brunette counterpart to a purple shampoo or conditioner, which is formulated for blondes instead; using this on blonde or gray hair would leave an unwanted dull or ashy cast rather than correcting anything.
It's meant to be used a couple of times a week rather than with every wash, since overuse can over-tone hair. It won't lighten hair or replace a colorist's toner — it's a maintenance step that keeps brassiness under control between salon visits.