Glossary
Technical terms relating to colour perception, standards and ColorAptitude™ — clearly explained.
Colour perception & physiology
Cones
Light-sensitive photoreceptors in the retina that detect colour (S-, M- and L-cones).
Opponent channels
Neural processing of colour in opposing pairs: red-green, blue-yellow and light-dark.
Colour constancy
The ability to perceive a colour as stable despite changes in illumination.
Chromatic adaptation
The visual system adapts to ambient light, causing colour perception to shift.
Metamerism
Two colours that appear identical under one light source but differ under another.
Inter-rater variation
Natural differences in colour perception and assessment between individuals.
Colour deficiency
Congenital or acquired impairment of colour perception (e.g. protanopia, deuteranopia).
Colour models & systems
CIE L*a*b*
Perceptually uniform colour model from CIE (1976) with a lightness axis (L*) and two colour axes (a*, b*).
OKLCH
Modern perceptually uniform colour model with better hue linearity than L*a*b*.
Munsell
Colour system based on visual uniformity: Hue, Value, Chroma.
ΔE / Delta-E
Standardised measure of the difference between two colours in a colour space.
CIEDE2000
The most modern ΔE formula (ISO/CIE 11664-6) with corrections for luminance, chroma and hue. ColorAptitude uses OKLCH-based distances internally and references CIEDE2000 only for cross-comparison with industry partners.
Hue circle
Circular arrangement of colour hues (0°–360°) in a colour model.
Colour assessment standards
FM100 (Farnsworth-Munsell 100 Hue Test)
The gold standard for measuring hue discrimination with 85 loose colour caps.
D-15 (Farnsworth Dichotomous)
Screening test with 15 colour caps to detect colour deficiency.
ASTM E1499-16
Standard for qualification of visual colour assessors, including FM100 and related procedures.
Anomaloscope
Optical instrument for precise diagnosis of red-green colour deficiencies (Rayleigh equation).
Ishihara
Well-known screening test with pseudoisochromatic plates for red-green colour deficiency.
Japanese Color Aptitude Test (Triangle Test)
Standardised colour aptitude test with 20 sets of three colour chips. Recognised by ASTM E1499-16 §6.3.2 / §6.4.2 as a complementary qualification instrument alongside FM100.
Magnitude Scaling
Psychophysical method for estimating the magnitude of colour differences — ASTM E1499-16 §6.4.
SPP (Standard Pseudoisochromatic Plates)
Pseudoisochromatic plate test for broad detection of colour deficiencies.
ColorAptitude™-specific
Attribution
Correctly identifying the three colour attributes: hue, chroma and lightness.
Hue discrimination
The ability to distinguish subtle hue differences — the core of colour perception.
Colour memory
The ability to remember a colour and later correctly recognise or reproduce it.
Calibration score
Score indicating how well your answers match the physical reference value.
Spiderwebdiagram
Radial chart showing your 3×3 colour profile in a single overview.
Mini-scan
Free screening test by ColorAptitude™ that in ~5 minutes gives an indication of your hue discrimination.