Blue shampoo. 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.

“Cool and neutral skin tones can wear most cool-toned blue hair colors, while warmer skin tones usually look the most natural with purple and ... These blue highlights look especially stunning ...

They’re capable of transforming shockingly-yellow bleached hair into silvery platinum and coaxing luscious cool ash tones from orange-tinged highlights ... purple neutralizes yellow while blue ...

Depending on your highlights and undertones ... navy blue and charcoal gray. Black hair looks amazing when teamed up with fire-engine red, cobalt blue or royal purple. Redheads look fabulous ...

The reality favorite has always loved experimenting with her hair color. Over the years Nicole's wowed with hot pink, bright blue, faded purple, and white-platinum locks, just to mention a few.