LESSON 20 · COLOUR

An apple is red, but almost none of the colours you paint on that apple are red. What lands on the canvas is the apple's own colour combined with the colour of the light hitting it. This is the single idea most self-taught artists never learn, and it is the difference between paintings that glow and paintings that look like flat drawings with colour poured on top.

SOFTWARE

Finish first: L15, L16, L18

• Your rendered sphere file from L16
• A desk lamp and a plain object — an egg, a ball, a mug — for a real-world check
• Photoshop, with a soft round brush and pressure controlling opacity

WATCH

Marco Bucci — The clearest explanation of local colour versus light colour that exists anywhere. Watch it twice — once before the lesson, once after.

Marco Bucci — Shows the same principle applied to the hardest case, where getting it wrong is most obvious.

THE LESSON

Local colour is the colour a thing is: a red apple, a white shirt, grey stone. It is what you would name if someone asked. Light colour is the colour of whatever is illuminating it: warm yellow from a lamp, cold blue-white from an overcast sky, orange from a fire. Every stroke you put down is the result of those two things meeting. You are never painting an object's colour. You are painting an object's colour under a particular light.

This is why the beginner method fails. Pick 'apple red', add white for the light side, add black for the shadow side, done. It produces a shape that is unmistakably red and unmistakably lifeless, because it contains no information about the light at all. Meanwhile a real white shirt in late afternoon sun contains orange, pink and violet, and hardly any white. If you photograph a white shirt at sunset and eyedropper it, you will not find white anywhere in the file.

Where light strikes a surface directly, the surface colour moves toward the colour of the light. A grey wall under a warm lamp goes warm. A red apple in the same light goes toward orange, because red plus yellow light heads that way. The stronger the light, the more it wins — under very bright sun, everything drifts toward the colour of the sun and objects with quite different local colours end up surprisingly close together. Light unifies.

It also drains saturation at the extreme. The very brightest spot, the specular highlight, is mostly the colour of the light source rather than the object, and on a shiny surface it is close to pure light colour. That is why blasting the highlight with a more saturated version of the local colour looks wrong. The peak of saturation is not in the brightest area and not in the deepest shadow. It sits in the transition — the halftone band just before the terminator, where the object is well lit but not overwhelmed. Aim your most intense chroma there.

A shadow is not an area with less colour. It is an area lit by a different light. Outdoors on a sunny day, the shadow side of an object is not lit by the sun, but it is lit by the enormous blue dome of the sky, plus bounce from the ground. So shadows outdoors are usually cooler and often bluer, while the lit side is warmer. Indoors under a warm lamp, the reverse can happen: the shadow picks up cool daylight from a window, or a warm bounce from a wooden floor.

The working rule is that shadows take their hue from whatever secondary light reaches them, and this usually contrasts in temperature with the key light. Warm light, cool shadow. Cool light, warm shadow. It is a strong tendency rather than a physical law, but as a starting assumption it will improve your work immediately.

So to move a colour into shadow: drop the brightness, shift the hue toward the ambient light's colour, and usually pull saturation down a little — but not to zero. Never mix in black. Black subtracts chroma and gives you the dusty, chalky look. If you find yourself dragging straight down the left-hand edge of the picker, stop and ask what is lighting that shadow.

None of this replaces Module 4. Work out the value plan first — where the lights, halftones, core shadow, reflected light and cast shadows sit — and only then decide the hues. If the value structure is right, a very wide range of colour choices will work. If it is wrong, no colour choice will save it. Value does the work; colour does the mood.

Photoshop lets you prove this in about a minute. Take your rendered grey sphere, then clip a Hue/Saturation adjustment layer to it (Layer > New Adjustment Layer > Hue/Saturation, tick Colorize, then Layer > Create Clipping Mask). Slide the hue around. The form holds together at every setting, because the values underneath are doing the work. Now paint the light side warm and the shadow side cool on a separate layer above, and watch the same sphere stop looking like a diagram and start looking like an object sitting in a room.

PRACTICE · 35 MIN

1. Open the L20 template. Three spheres are outlined on a shared ground plane, all lit from the upper left.
2. Decide your light: a warm lamp at roughly H40. Write the number in the corner with the Type tool.
3. Assign local colours: sphere 1 white, sphere 2 red, sphere 3 dark blue. Block each in flat at its shadow value first.
4. Paint the lit side of each sphere by moving its local colour toward H40 and raising brightness. The white sphere should end up warm cream, not white.
5. Paint the shadow side of each by lowering brightness and shifting the hue the opposite way, toward roughly H210.
6. Put your most saturated stroke on each sphere in the halftone band just before the terminator, not in the highlight.
7. Add the cast shadows on the ground plane, using the ground's local colour shifted the same cool direction.
8. Set up your desk lamp, put a real object under it, and compare. Fix anything the real thing disagrees with.

Done when: Three spheres of clearly different local colours read as sitting in the same room under the same lamp. Sample the lit side of each with the eyedropper: all three hue numbers should have moved toward the light's hue, and all three shadows toward the ambient hue.

Download these and work along with the lesson.

CHECK YOURSELF

Answer out loud first, then open each one to compare.