How color placement (not the color itself) can add visual width or narrowness to specific parts of the face.
It's About Contrast Placement, Not the Color Itself
Hair color affects perceived face shape primarily through where light and dark tones sit relative to your face — a face-framing money-piece of lighter color near the cheekbones draws the eye to that area and can visually widen it, regardless of whether the base color is blonde, brunette, or anything else.
Darker Money Pieces Near the Jaw
Conversely, a darker lowlight or color placed specifically along the jawline can make that area recede slightly in the eye, similar in principle to makeup contouring but achieved through color rather than shading.
Combine With Your Face-Shape Guide
Use your specific face-shape guide's 'add width here' or 'minimize width here' guidance to decide where a stylist should place lighter versus darker color — the same balancing logic used for haircuts and makeup applies to strategic color placement.