Colour Recommendation You Rêve Paris: Find Your Perfect Nail Shade with a Scientific Approach

Choosing the perfect nail polish colour isn't just about taste — it's a science. Colourimetry, the discipline that studies the measurement and harmony of colours against human appearance, relies on objective principles: your skin undertone (warm, cool or neutral), skin depth, hair colour and eye colour all work together to determine which shades flatter you most. At You Rêve Paris, a nail salon in the 1st arrondissement of Paris, we wanted to make this expertise accessible to everyone — for free, with no appointment needed.

The Science Behind the Colour: What Is Beauty Colourimetry?

Colourimetry in cosmetics is built on decades of dermatological and colour theory research. The fundamental concept is simple: certain nail polish colours create a natural visual harmony with your complexion, while others can make you look tired or dull — not because the colour is "bad", but because it doesn't match your personal colourimetric profile.

The most important parameter is your skin undertone: the underlying hue of your skin, independent of sun exposure. There are three categories:

• Warm undertone: golden, yellow or peach dominant. Coral, soft orange, tomato red and brown shades flatter you.
• Cool undertone: pink, blue or red dominant. Blues, fuchsias, blue-based reds and soft pinks are your natural allies.
• Neutral undertone: a balance between warm and cool. You're lucky enough to wear almost any shade — from soft nudes to bold reds.

How Does Our Colour Recommendation Tool Work?

Our colour recommendation tool follows a rigorous scientific process in several stages, fully automated and executed in your browser:

Step 1 — Facial Detection

Using the face-api.js library (powered by TensorFlow.js), our tool detects your face and 68 facial landmark points in real time. This detection precisely identifies the skin areas to analyse: cheeks, forehead and chin — areas least affected by temporary redness or direct sun exposure.

Step 2 — Skin Analysis and Undertone Classification

The tool samples 6 skin zones and calculates average RGB values for each sample. Outliers (areas that are too light or too dark) are statistically filtered. Then:

• RGB → CIELAB colour space conversion — the international standard for colour measurement.
• ITA index calculation: ITA = [arctangent((L* − 50) / b*)] × (180 / π). This index classifies your skin according to the international dermatological standard.
• Undertone determination (warm/cool/neutral) based on the b* axis of CIELAB (blue-yellow axis).
• Depth classification: very light, light, medium, dark or very dark.

Step 3 — Hair and Eye Detection

The algorithm also analyses hair and eye regions to classify your hair colour (blonde, brown, brunette, black, red, grey) and eye colour (blue, green, hazel, brown, black). These two parameters feed into the overall harmony calculation.

Step 4 — Multi-Criteria Evaluation

This is where the magic happens. Every shade in our salon's OPI selection (~200 shades in semi-permanent and classic polish) is evaluated using a deterministic scoring algorithm — meaning the same input profile will always produce the same result. No randomness, no generative AI: a reproducible, objective calculation.

Our recommendation engine draws on the foundational work of the Commission Internationale de l'Éclairage (CIE) on the CIELAB colour space, as well as dermatological research around the ITA (Individual Typology Angle) developed by Guermond et al. for objective skin type classification. It also integrates principles from the colourimetric seasonal calendar (spring, summer, autumn, winter), popularised by Carole Jackson in "Color Me Beautiful".

The criteria evaluated include:

• Undertone match: the primary criterion — a cool shade on a cool undertone is harmonious.
• Skin depth: lighter skin is flattered by soft shades, deeper skin by rich, saturated colours.
• Seasonal harmony: inspired by the colourimetric seasonal calendar.
• Colour intensity: contrast between your profile and the shade's saturation.
• Hair harmony: does your hair colour reinforce or contradict the proposed shade?
• Eye match: certain nail shades make your natural eye colour pop.
• Age factor: subtle adjustment based on estimated age.
• Style and vibe: classic, bold, natural — does the shade's "character" match the detected profile?

Step 5 — Selection of the Top 3 Shades

After scoring, the algorithm selects the top 3 shades, ensuring they come from different colour families — giving you a coherent but varied range of choices (for example: a nude, a pink and a red).

The Final Choice Is Always Yours

It's important to emphasise: our colour analysis tool is a guide, not a rulebook. The recommendations are scientifically grounded, but beauty is also about personal preference, mood, style and context.

Love a colour the tool doesn't recommend? Brilliant! Wear what makes you happy. The goal isn't to box you into rules — it's to give you an informed starting point to explore our OPI salon selection with confidence.

How to Use the You Rêve Paris Colour Analysis Tool

Using it couldn't be simpler:

1. Visit our You Rêve Paris colourimetry page.
2. Allow camera access (or upload a selfie) — no photo storage, your privacy is respected.
3. The tool detects your face in seconds and runs the analysis.
4. Discover your 3 recommended OPI shades with your full profile breakdown: undertone, depth, ITA, hair and eye colour.
5. Book directly with the shade you love, or visit the salon for personalised advice.

Why Did We Create This Tool?

At You Rêve Paris, we see clients hesitate in front of our OPI wall every day. "I never know which colour to pick" is the phrase we hear most. We wanted to solve this problem with a scientific, accessible approach.

Our tool combines:

• The rigour of scientific colourimetry (CIELAB standard, ITA index)
• The power of facial detection (face-api.js, TensorFlow.js)
• Our expertise as a professional nail salon in central Paris

The result: a personalised colour advisor, free and instant, that complements (without replacing) the human expertise of our salon technicians.

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