Losing vibrancy is another challenge with adding highlights to dark tones. "Black hair reflects the light best, and over time, you will lose some of that gorgeous shine," explains Michael.

While it usually occurs in dark ... the best purple shampoos are formulated to quell the problem—often upon first wash. The best purple shampoos refine blonde, gray and platinum hair tones ...

According to Emily Claire, a Davines colorist at Rob Petoom, cobalt-colored formulas are more effective than their purple counterparts for maintaining highlights on darker hair. “[In general ...