By Rehues Editorial Team | April 2026
If you've ever watched your freshly bleached, highlighted, or ash-toned hair turn an unwanted shade of yellow or brassy orange within a few weeks, you already know the frustration. Purple shampoo is the most talked-about solution — but what does it actually do, and is it the right product for your hair? This guide breaks down the science, explains who genuinely benefits, and introduces why the Rehues Colour Lock Shampoo is a compelling alternative for colour-treated hair in Singapore.
The Science Behind Purple Shampoo
To understand why purple shampoo works, you need to revisit a concept from basic colour theory: the colour wheel. Colours that sit directly opposite each other on the wheel are called complementary colours, and when mixed together, they cancel each other out.
Yellow and violet sit directly opposite. That means violet pigments neutralise yellow tones — and since brassiness in bleached or highlighted hair typically manifests as yellow or orange, a shampoo containing violet pigments is an elegant and effective solution. The violet particles deposit onto the hair shaft during washing, counteracting warmth and restoring a cooler, more neutral tone.
This is not a permanent colour change. Purple shampoo does not bleach or lighten. It is a toning tool: a way to maintain the cool, bright result you left the salon with, rather than a way to change your hair colour altogether.
How Pigment Deposits Work During a Wash
When you apply a colour-depositing shampoo to wet hair, the cuticle — the outermost protective layer of each strand — is slightly lifted by water and heat. This temporary opening allows small pigment molecules to penetrate slightly into the cortex or adhere to the surface of the cuticle. The longer you leave the product on, the more pigment deposits. Rinse too quickly and you get subtle toning; leave it on for the full recommended time and the effect is more pronounced.
The key is consistency. Because the pigment deposits gradually wash out with each subsequent wash, you need to use a toning shampoo regularly to maintain the effect.
Who Actually Needs Purple (or Toning) Shampoo?
Not everyone needs a purple shampoo, and using it on the wrong hair type can actually dull your colour rather than enhance it. The candidates who benefit most are:
Bleached and pre-lightened hair — the bleaching process strips natural melanin, leaving the underlying warm tones exposed. Without toning, bleached hair almost always skews yellow or orange within weeks.
Highlighted hair — balayage, foil highlights, and babylights all involve pre-lightening sections of the hair. Those lightened sections are susceptible to the same brassiness that affects fully bleached hair.
Silver and grey hair — natural grey and silver hair can develop a yellowish cast from environmental factors including UV exposure, pollution, and even mineral build-up from tap water. Violet toning counteracts this yellowing and keeps grey hair looking crisp and bright.
Ash-blonde and platinum hair — these shades are deliberately cool-toned and sit very close to the yellow end of the spectrum, meaning even minor tonal drift looks dramatic. Regular toning is practically non-negotiable.
If your hair is naturally dark or you have a warm-toned dye job (think golden blonde, copper, or auburn), a toning shampoo is unlikely to do much for you and may actually mute your colour. Those hair types need different colour-care strategies entirely.
Singapore's Climate Makes Brassiness Worse
In Singapore, colour-treated hair faces challenges that many global guides simply don't account for. The average temperature hovers around 31–32°C year-round, humidity is consistently above 80%, and UV exposure is intense every single day, not just in summer.
UV radiation in particular is one of the primary drivers of colour fade and brassiness. It breaks down the dye molecules sitting in your hair shaft, and because warm pigments (yellow, orange, red) are more stable than cool pigments (violet, blue, ash), what's left behind after UV degradation tends to skew warm. The result is brassiness — even if you started with a beautifully cool, neutral tone.
Frequent washing, which is common in Singapore's heat, compounds the problem. Every wash cycle removes some of the pigment deposited by your toning shampoo, which means you need a product that both tones and protects — not just one or the other.
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How the Rehues Colour Lock Shampoo Works as a Toning Shampoo
The Rehues Colour Lock Shampoo contains Ext. Violet 2, the same category of violet pigment found in dedicated purple shampoos. Applied to bleached, blonde, highlighted, or silver hair, it deposits cool violet tone during each wash to neutralise brassiness and maintain the cooler colour you want.
But where Rehues goes further than a standard toning shampoo is in the supporting ingredient technology. The formula contains the brand's proprietary Colour Lock Blend™, which is specifically engineered to target tone fade and neutralise brassiness at a structural level — not just on the surface. Alongside this, the Bond Repair Complex works to rebuild broken protein bonds within the hair shaft, which are routinely damaged during bleaching and colouring processes.
The ingredient list also includes Panthenol (Pro-Vitamin B5), which penetrates the cortex to improve moisture retention and add flexibility; Sodium Hyaluronate (a low-molecular-weight form of hyaluronic acid) for deep hydration; Amodimethicone, a lightweight silicone that smooths the cuticle and improves manageability; and Sophora Angustifolia Root Extract, a botanical that soothes the scalp. The surfactant used is Cocamidopropyl Betaine — a gentle, sulphate-free cleansing agent that removes build-up without stripping colour or natural oils.
There are no sulphates (SLS or SLES) and no parabens in the formula. This matters specifically for colour-treated hair because sulphates are one of the primary culprits behind accelerated colour fade. Every time you wash with a sulphate-heavy shampoo, you're essentially pulling colour pigment out of the hair shaft with the same force it uses to strip oil and dirt.
How to Use a Toning Shampoo Correctly
The single most common mistake people make with purple or toning shampoo is using it incorrectly — either not leaving it on long enough to work or using it so frequently that it overtones and turns the hair a dingy grey-purple.
Apply the Rehues Colour Lock Shampoo to thoroughly wet hair. Distribute it evenly from root to tip and leave it on for three to ten minutes before rinsing. The three-minute mark gives you subtle, natural-looking toning. Ten minutes delivers more pronounced violet correction, which is appropriate when you're dealing with heavy brassiness.
Frequency matters as much as technique. For most people with bleached or highlighted hair, using a toning shampoo one to two times per week is sufficient. On the days in between, a colour-safe, sulphate-free shampoo maintains cleanliness without aggressively stripping either your toning work or your base colour. Using a toning shampoo every single day is likely to build up excessive violet pigment and produce a dull or purple-tinged result rather than the clean, neutral tone you're after.
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Building Your Toning Routine in Singapore
Given how quickly colour can shift in Singapore's climate, consistency is your best tool. A sensible weekly routine might look like this: tone with the Rehues Colour Lock Shampoo once or twice a week, follow each wash with a colour-safe conditioner, and incorporate a weekly deep treatment to replace the moisture that colouring processes remove. Protecting your hair from UV on sunny days — which in Singapore means essentially every day — extends the life of any toning work you've done.
Rehues is currently running a Mother's Day Sale with up to 50% off sets and free SG shipping, which makes this a good moment to pick up the Colour Lock Shampoo alongside other colour-care essentials from the range.
Conclusion
Purple shampoo works through straightforward colour science: violet neutralises yellow. For anyone with bleached, highlighted, blonde, silver, or ash-toned hair — especially in a climate as UV-intense and humid as Singapore's — a toning shampoo is not optional; it's a fundamental part of maintaining your colour between salon visits. The Rehues Colour Lock Shampoo delivers that violet toning alongside a sulphate-free, bond-repairing formula that treats the hair as well as it tones it. Used correctly — two to three minutes for subtle results, up to ten for stronger correction, one to two times per week — it keeps brassiness in check without overtoning.
Frequently Asked Questions
Can I use purple shampoo every day on colour-treated hair in Singapore?
Using purple shampoo daily is not recommended, even in Singapore's humid climate where brassiness develops quickly. Daily use deposits too much violet pigment onto the hair shaft, which can leave bleached or blonde hair with a dull grey or purple cast rather than a clean, neutral tone. The Rehues Colour Lock Shampoo is designed for two to three uses per week — enough to maintain tone without over-depositing — and is sulphate-free so it won't strip your colour on the other wash days.
What does purple shampoo actually do to your hair?
Purple shampoo works through complementary colour theory: violet pigment cancels out yellow and brassy tones on the hair shaft, neutralising the warm tinge that develops as bleached, highlighted, or ash-toned hair oxidises. It does not bleach, lighten, or structurally alter your hair — it simply deposits toning pigment during each wash to counteract unwanted warmth. In Singapore's high-UV, high-humidity environment, oxidation and brassiness accelerate significantly, making a toning shampoo an especially important part of the colour maintenance routine.
How long should I leave purple shampoo on for the best results?
Three to five minutes is sufficient for regular maintenance toning. If your hair has developed noticeable yellow or brassy tones, leaving the shampoo on for up to ten minutes allows more pigment to deposit for stronger correction. Avoid leaving it on beyond ten minutes regularly, as this increases the risk of over-toning — particularly on bleached or porous hair, where pigment is absorbed more readily.
Does purple shampoo work on Asian hair?
Yes — purple shampoo works on any pre-lightened or lightened Asian hair that has developed yellow or brassy tones. Many Singaporeans with bleached, highlighted, or ash-toned hair experience rapid brassiness due to the intense UV exposure here, and a violet toning shampoo addresses this effectively. The Rehues Colour Lock Shampoo is formulated for all hair types, making it suitable for the Asian hair texture that is common in Singapore.
What is the difference between purple shampoo and a colour-depositing shampoo?
Purple shampoo is a type of colour-depositing shampoo — it deposits violet pigment specifically to neutralise yellow and brassy tones. Colour-depositing shampoos, in contrast, come in a range of shades (including pink, brown, grey, and blue-violet) and are designed to refresh or maintain specific colour tones rather than simply neutralising unwanted warmth. The Rehues Colour Lock Shampoo range includes both the Blue shade (for toning and brassiness correction) and other shades for actively maintaining different colour families.
