# Colour as Pigment and Colour as Light

Painting I · Colour, Perception and Materials · https://tryals.app/learn/painting-i/colour-as-pigment-and-colour-as-light

## Two Ways to Make a Colour

Overlap two beams of light and the mixture is **lighter** than either beam. Mix two paints on a palette and the result is **darker**.

**Additive mixing** combines emitters:
- Light sources add their power together.
- Red, green, and blue light combine to make white.
- Newton showed that colour is already in the light.
- Hermann Grassmann formalised these rules in **1853**.

**Subtractive mixing** combines filters:
- Pigments absorb specific wavelengths and reflect the rest.
- A mixture must pass **both** filters, multiplying their reflectances.
- The result reflects less light, making paint mixtures darker.

| System | What combines | Primaries | All three combined |
|---|---|---|---|
| Additive | Light beams | Red, green, blue | White |
| Subtractive | Colourant layers | Cyan, magenta, yellow | Near-black |
| Painters' | Paint tubes | Red, yellow, blue | Dark brown |

Red, yellow, and blue are simply a **workshop convention** from the 1720s. Cyan and magenta are the true subtractive primaries.

### The Munsell System

Any colour answers three independent questions. Albert Munsell organised them in **1905**:

| Property | Question | Scale |
|---|---|---|
| **Hue** | Which colour family? | **10** major hues arranged in 100 steps |
| **Value** | How light or dark? | 0 for black up to **10** for white |
| **Chroma** | How intense or pure? | 0 for neutral grey, extending past **20** |

These three dimensions are fully independent. You can adjust one while holding the other two constant.

Value is perceptually non-linear. A value of 5 looks halfway to white, but it reflects only **a fifth** of incident light. The human eye compresses luminance heavily.

> **Common pitfall:** Confusing the three dimensions. People often say "brighter" when they mean higher value, higher chroma, or a shifted hue. Identify which property you need to change before mixing.

## Practice questions

10 of this lesson's 14 practice questions, with answers. The full set is in the app.

### 1. A student mixes ultramarine and cadmium yellow and gets a green darker than either tube. In the lighting rig she then aims a blue lamp and a yellow lamp at one patch of white wall and gets something paler than either lamp alone. Why do the two mixtures run in opposite directions?

A. Pigment subtractively filters light, whereas overlapping lamp beams add power.
B. A white wall reflects every wavelength far better than any dark palette board.
C. High lamp flux temporarily saturates cone cells, desaturating perceived colour.
D. Blue and yellow are complementary light beams, but act as lower-chroma paints.

**Answer:** A. Pigment subtractively filters light, whereas overlapping lamp beams add power.

**Why:** Because the arithmetic is different. Two pigments each return a fraction of the incident light, and the mixture returns roughly the product of the fractions, which is always smaller than either. Two lamps each deliver power, and the powers add. Brightness of the source, surface reflectivity, and the choice of complements change nothing about that fundamental difference.

Page: https://tryals.app/practice/painting-i/colour-as-pigment-and-colour-as-light/a-student-mixes-ultramarine-and-cadmium-yellow-and-gets-a-green

### 2. Sort each observation by the mixing system it belongs to.

**Answer:**

- Additive mixing of light: Red and green together read as yellow, All three primaries together give white, The primaries are red, green and blue
- Subtractive mixing of colourant: The result is always darker than the darker of the two parents, A cyan and a magenta layer together return only blue, Enough mixing converges on a dark neutral

**Why:** The two columns are opposite in direction and identical in method: in both cases you are asking what survives. In light, everything survives and accumulates. In paint, only what both layers happen to return survives, and each new addition can only take away more.

Page: https://tryals.app/practice/painting-i/colour-as-pigment-and-colour-as-light/sort-each-observation-by-the-mixing-system-it-belongs-to

### 3. Cyan and yellow paint mix to green because green is the only band that both pigments return.

**Answer:** True

**Why:** **True.** Cyan absorbs red and returns green and blue; yellow absorbs blue and returns red and green. Green is the only band left standing after both, so green is what comes back. That reasoning is the whole of subtractive mixing and it works for any pair once you know what each absorbs.

Page: https://tryals.app/practice/painting-i/colour-as-pigment-and-colour-as-light/cyan-and-yellow-paint-mix-to-green-because-green-is-the-only-band

### 4. Complete the vocabulary of colour systems.

**Answer:** Newton published Opticks, which argued that the colours are already present in white light, in **1704**. Albert Munsell separated hue, value and **chroma** in his notation of 1905. The primaries of subtractive mixing are cyan, **magenta** and yellow. Two hues lie **50** steps apart on Munsell's circle of a hundred when they are complementary in his system.

**Why:** The first two distractors are the traps worth naming. 1666 is when Newton did the prism work and 1704 is when he published it, and the two dates are nearly forty years apart. "Saturation" and "chroma" are close but not interchangeable: chroma is Munsell's own scale, measured against a neutral of the same value.

Page: https://tryals.app/practice/painting-i/colour-as-pigment-and-colour-as-light/complete-the-vocabulary-of-colour-systems

### 5. Which of these are true of Munsell's three dimensions?

A. Value runs from 0 for black to 10 for white
B. Chroma has a fixed upper limit that is the same for every hue
C. Hue, value and chroma can each be changed while the other two are held
D. A value 5 grey returns roughly a fifth of the light falling on it, not half

**Answer:** A. Value runs from 0 for black to 10 for white; C. Hue, value and chroma can each be changed while the other two are held; D. A value 5 grey returns roughly a fifth of the light falling on it, not half

**Why:** The fourth is wrong and usefully so: chroma is open-ended and the reachable maximum differs by hue and by pigment, which is exactly why a system with a fixed saturation axis misrepresents what a palette can actually do.

Page: https://tryals.app/practice/painting-i/colour-as-pigment-and-colour-as-light/which-of-these-are-true-of-munsells-three-dimensions

### 6. Match each term to what it names.

**Answer:**

- Additive mixing → Combining emitters, so that the powers sum
- Subtractive mixing → Combining filters, so that the fractions multiply
- Chroma → Distance from a neutral grey of the same lightness
- Value → How much light a surface returns, on a scale of 0 to 10

**Why:** Keeping these four apart disposes of most palette confusion. The two operations differ in arithmetic, not in kind; the two dimensions differ in what they are measured against, chroma against a neutral of equal value and value against black and white.

Page: https://tryals.app/practice/painting-i/colour-as-pigment-and-colour-as-light/match-each-term-to-what-it-names

### 7. Arrange the steps of matching a colour by eye in the order a painter carries them out.

**Answer:**

1. Judge the target's value against a neutral grey scale
2. Name the hue family the target belongs to
3. Judge how far from neutral the target sits
4. Mix a first approximation from the fewest tubes that can reach it
5. Hold the mixture edge to edge against the target and correct the property that is furthest out

**Why:** Value first is not a preference: it is the property the eye judges most reliably and the one that cannot be repaired later without disturbing the other two. The final step matters because a colour held apart from its target is always judged wrongly, and edge to edge is the only honest comparison.

Page: https://tryals.app/practice/painting-i/colour-as-pigment-and-colour-as-light/arrange-the-steps-of-matching-a-colour-by-eye-in-the-order-a-painter

### 8. A Munsell value 5 grey looks halfway between black and white. What percentage of the light falling on it does it actually return?

**Answer:** 20 (within ±5)

**Why:** About **20 per cent**. Halfway in appearance is nowhere near halfway in physics, because the visual system compresses a huge range of luminance into a manageable scale of lightness. That gap is why a photographic grey card sits near a fifth reflectance and not a half.

Page: https://tryals.app/practice/painting-i/colour-as-pigment-and-colour-as-light/a-munsell-value-5-grey-looks-halfway-between-black-and-white-what

### 9. Red, yellow and blue are the primaries of subtractive mixing in the same sense that red, green and blue are the primaries of additive mixing.

**Answer:** False

**Why:** **False.** The subtractive primaries are cyan, magenta and yellow, which is what every printing process uses. Red, yellow and blue is a studio convention inherited from the eighteenth century, and its limits are visible: an RYB palette cannot mix a clean turquoise or a clean pink at all.

Page: https://tryals.app/practice/painting-i/colour-as-pigment-and-colour-as-light/red-yellow-and-blue-are-the-primaries-of-subtractive-mixing-in-the

### 10. A painter attempts to make an intense yellow duller without changing its lightness or colour family. Munsell defines these properties as fully independent dimensions. What precise physical adjustment does this demand?

A. Increasing black pigment to lower both value and hue
B. Lowering value while maintaining constant hue only
C. Reducing chroma while keeping hue and value fixed
D. Shifting the hue step while preserving overall value

**Answer:** C. Reducing chroma while keeping hue and value fixed

**Why:** Confusing chroma with value or hue is common because darkening often desaturates colour in practice. However, dulling a colour without altering lightness or family isolates chroma entirely. Adding black alters value, and shifting hue changes the family itself.

Page: https://tryals.app/practice/painting-i/colour-as-pigment-and-colour-as-light/a-painter-attempts-to-make-an-intense-yellow-duller-without-changing