Colour

Learn about colour!

colour space

numerical description of colour detectable by the human visual system

colour space example 1

RGB for digital displays, an additive model

colour space example 2

CMY for paints and dyes, subtractive model

luminance/ value

the contrast of a single hue from dark to light

what is colour luminance/ value good for

ordered data

luminance and saturation rule of thumb 1

do not use them for representing more than 5 numeric values

luminance rule of thumb 2

ensure luminance contrast with the background when showing symbols, text or detailed graphics

saturation

the purity/ colourfullness of a hue

what is colour saturation good for?

ordered data

saturation, luminance and hue all suffer from?

low accuracy of perceiving the variable in non-contiguous regions - the background matters!

how does saturation interact with size?

it is more difficult to perceive saturation in small regions - not separable

saturation rule of thumb 2

use more saturated colours when coding small regions like lines or symbols, use less saturated colours when coding large regions like backgrounds

hue

the “true colour”

what is colour hue good for?

categorical data

hue interaction with size

more difficult to distinguish between small marks - the higher the spatial frequency, the less saturated the colour appears

hue rule of thumb 1

do not use more than 7 different hues

hue rule of thumb 2

use conventional hues that people know how to name

transparency

encoding information by decreasing the opacity of a mark

transparency separability

not separable from other colour variables, strong interactions with luminance and saturation

when is transparency typically used?

in conjunction with hue in small steps (typically two)