Guides

Warm or cool hair colour: which suits your undertone?

Pick the temperature of your hair colour by the contrast you want against your skin, not by a rule that warm skin needs warm hair. If you are not sure of your undertone, a neutral shade close to your current depth is the safe choice. Decide temperature, depth and dimension as three separate questions.

Updated October 20, 2026

What is the difference between warm, cool and neutral hair colour?

Warm and cool describe the cast of the colour, not how light or dark it is. A dark cool brown and a dark warm brown sit at the same depth; a colourist calls the difference tone or temperature.

How do you tell your undertone, and how sure can you be?

1. Use daylight from a windowIndoor bulbs tint everything yellow or blue. Stand facing a window, no direct sun, no filter.
2. Hold something white next to your faceA white shirt or sheet of paper gives your eye a reference. Against it, skin leans golden or olive, pink or rosy, or neither.
3. Look at the inside of your wrist and at jewelleryVeins that read greenish and gold that looks at home point warm; veins that read bluish and silver that looks at home point cool. These are rough cues, not measurements.
4. Check how your current colour behavesIf your hair always drifts brassy, your base is warm. If ash tones look natural on you, your undertone probably agrees.
5. Decide how confident you areIf two cues disagree, treat your undertone as uncertain and start from neutral. Certainty is not required to choose well.

Phone photos are an estimate. The International Commission on Illumination published a standard in 2025 for measuring human skin colour precisely because the result changes with illumination, body location and method. A selfie under mixed light can move an undertone reading from warm to neutral on its own, so an app that sounds certain about your undertone from one photo is guessing. Tressaly treats low confidence as a reason to recommend a neutral or subtle dimensional change rather than a strongly warm or cool one.

Does warm skin need warm hair?

No. Matching is one option and contrast is another, and both are used deliberately. A warm honey on warm skin reads soft and continuous. A cool ash on the same skin reads sharper and makes the skin look warmer by comparison. Neither is correct; they are two effects, and the question is which one you want to see around your face. If a colour analysis placed you in the cool, high contrast Winter season, hair colour for a Winter skin tone goes through the shades by Deep, True and Bright Winter.

Olive undertones are the common case where the rule misleads. Olive mixes a green or yellow cast with neutral depth, so very golden shades can push the skin toward sallow and very icy ash can read flat. Colourists commonly steer olive skin toward neutral and neutral cool browns, soft mushroom tones and, when a warm effect is wanted, red based rather than yellow based warmth. That is experience rather than a measurement, and it is a starting point to preview, not a law.

Why decide depth and dimension separately?

Depth is how light or dark the colour is. Dimension is how much it varies: highlights, lowlights, a shadowed root. Temperature is the cast. Changing one of the three at a time is the lowest risk move, and changing temperature alone, at your current depth, is the easiest to live with and to reverse.

Large lifts and strong tone changes are salon results. They depend on the condition of your hair, on what has been applied before and on the colourist's judgement. A preview can show the idea of a shade next to your skin; it cannot promise what a chemical process will produce on your hair. Tressaly labels those changes as salon results for that reason, and it keeps your skin as it was, so the colour, not a filter, is what you are judging.

Should you follow a colour trend like cherry red?

Pinterest named Cherry Coded a 2025 direction and listed Cherry Red in its 2025 palette, and L'Oreal Professionnel built a campaign on deep cherry shades. Cherry is a useful example because it comes in two temperatures: a blue based cherry is cool, an orange based cherry is warm. The trend tells you the family; the version you choose should still follow the contrast you want and the depth you can maintain. Tressaly does not push a trend colour on its own, and it never assigns a colour by undertone or by anything it guesses about you.

Guides describe styling choices, not medical or dermatological advice. Tressaly reads one selfie and shows these choices on your own photo. How a read works.