Unit 08.00: Colour that carries meaning, and colour that does not

Colour either encodes something or costs the reader attention for nothing.

The telephone test

Describe the chart over the phone. Anything you have to say about colour is information colour carries; anything you never mention was decoration.

The code sorts six uses of colour by what each encodes.

USES = [
    ("one series, one colour",              "no meaning", "colour is decoration"),
    ("categories in distinct hues",         "identity",   "hue = which group"),
    ("a value from low to high",            "quantity",   "lightness = how much"),
    ("one highlighted, rest grey",          "emphasis",   "colour = look here"),
    ("every bar a different colour",        "none",       "rainbow with no meaning"),
    ("red for bad, green for good",         "valence",
     "meaningful, and fails for colour-blind readers"),
]
print(f"{'use of colour':34} {'encodes':10} note")
for use, encodes, note in USES:
    print(f"{use:34} {encodes:10} {note}")

print("\nIf removing the colour loses no information, the colour was decoration.")

# The test: describe the chart over the phone. Anything you have to say about
# colour is information the colour carries; anything you do not mention was
# decoration, and it cost the reader attention.

Four of the six encode something real: identity, quantity, emphasis, valence. Two encode nothing - a single-series chart in blue, and a rainbow of bars where the categories have no order.

The red/green row is the awkward one. It genuinely carries meaning and it fails for around one in twelve men, which is the subject of the next two units.

The mistake this prevents

The mistake is choosing a palette before deciding what colour is for. Hue distinguishes categories and lightness shows quantity - using hue for a quantity produces a chart nobody can order without the legend.

Takeaway

Colour must encode identity, quantity or emphasis. If removing it loses no information, it was decoration and it cost the reader attention.

Mark complete