The short answer: Gray hair is extra susceptible to brass and traditional purple shampoos do little to address the metals + minerals causing that brass. TripleBright oxidation defense purple shampoo mitigates the metal and mineral buildup that causes discoloration and roughness in gray hair.

Gray hair has a reputation for being low-maintenance, but in reality…it’s quite the opposite. Without pigment as a buffer, your grays end up revealing everything—every environmental exposure, every mineral deposit, every shift in tone—faster, and more visibly, than pigmented or colored hair. Over time that buildup can lead to an unwanted brassy cast that dulls hair’s natural shine.

traditional purple shampoos of the past

For decades, the default response to brass has been purple shampoo—a quick, familiar solution rooted in color theory that’s widely accepted as the essential maintenance tool for anything lightened, blonde, gray, or white. It can work (temporarily), but the results are often uneven (if you’ve ever seen your grandma suddenly sporting lavender hair like she’s the lead singer in an indie band, the cause is often staining from purple shampoo).  

“Because gray hair lacks melanin, there’s no underlying pigment to absorb or mask the chromophores that develop from environmental exposure–so yellowing presents more clearly,” explains Jessica Pierre, K18’s principal formulator. “Traditional purple shampoos deposit violet pigments onto the hair’s cuticle surface, where they optically neutralize warm tones, but the effect is purely visual and surface-level.”

K18’s breakthrough formula, TripleBright oxidation defense purple shampoo, offers a more 360 approach to brighter, longer-lasting blonde. Rather than simply cancelling out the appearance of yellowing/brass with a temporary layer of color, it addresses what’s causing gray hair to lose its brightness in the first place.

the real, hidden cause of yellow + orangey tones

The buildup on our hair fibers isn’t always visible to the naked eye, but it is chemically active, and often unavoidable.

Trace metals such as copper and iron—both commonly present in unfiltered tap and well water—bind to the hair and catalyze oxidative reactions, gradually producing the yellow tint associated with brassiness. At the same time, hard water minerals like calcium and magnesium deposit along the cuticle, leaving behind a film that dulls tone and alters texture, making hair feel stiffer, drier, and more difficult to manage.

This is where traditional purple shampoos hit a wall. They neutralize the orangey tones you can see, but leave the buildup on the actual fiber intact, which in turn creates an inescapable cycle of dulling and color fade. 

TripleBright works totally differently, combining tone correction with removal and prevention of future brass + yellow through K18’s triple-action technology. 

Ionic detox instantly removes brass-causing metals + minerals, leaving it feeling clean, soft, and manageable, precision violet technology neutralizes any remaining warmth without staining or overtoning and a biopolymer seals in results, defending against future buildup by limiting the reattachment of those same particles over time.