Color Glossary

Additive Color

Color created by combining colored light. Screens use additive color — RGB (red, green, blue). All three combined at full intensity produce white.

Alpha Channel

The transparency component of a color, ranging from 0 (fully transparent) to 1 (fully opaque). Represented in CSS as RGBA or 8-digit HEX.

Analogous

A color harmony using colors adjacent on the color wheel — typically within 30° to 60° of each other. Creates calm, cohesive palettes.

APCA

Advanced Perceptual Contrast Algorithm. A newer alternative to WCAG's contrast ratio formula that better accounts for how human vision perceives contrast. Not currently part of WCAG 2.2.

Brightness

How light or dark a color appears. In HSL, called lightness (L). In HSV, called value (V).

Chroma

The purity or intensity of a color — how far it is from gray. Similar to saturation but defined differently in some color spaces (notably Munsell).

CIE Lab

A perceptual color space developed by the International Commission on Illumination. Designed so equal numerical distances correspond to equal perceived differences — used for color difference calculations (Delta E).

CMYK

Cyan, Magenta, Yellow, Key (black). A subtractive color model used in printing. Each value represents the amount of ink applied, from 0% to 100%.

Color Blindness

Color vision deficiency (CVD) — reduced ability to distinguish certain colors. Affects roughly 1 in 12 men and 1 in 200 women worldwide. Most common types: protanopia (red-blind), deuteranopia (green-blind), tritanopia (blue-blind).

Color Harmony

A combination of colors that looks pleasing together. Based on the geometric relationship of colors on the color wheel.

Color Space

A mathematical model for describing colors. Common color spaces include sRGB, Adobe RGB, Display P3, ProPhoto RGB, and CMYK. Each has a different gamut.

Color Wheel

A circular arrangement of hues showing their relationships. The foundational tool of color theory. Digital color wheels use HSV hue distribution.

Complementary

Two colors directly opposite on the color wheel (180° apart). Creates maximum contrast and visual tension. Blue and orange is the classic example.

Contrast Ratio

A number expressing the luminance difference between two colors, from 1:1 (identical) to 21:1 (black on white). Used for WCAG accessibility compliance.

Delta E (ΔE)

The standard measure of perceptual color difference. Below 1 is imperceptible; 1-2 is only noticeable side by side; 10+ is clearly different. Based on CIE Lab color space.

Deuteranopia

A type of color blindness where green cones are missing. Colors are perceived primarily in blue and yellow. The most common type of red-green color blindness.

Gamut

The range of colors a device or color space can reproduce. sRGB has a smaller gamut than Display P3 or Adobe RGB. CMYK has a smaller gamut than RGB — some screen colors cannot be printed.

Gamma

The nonlinear relationship between color values and displayed brightness. Used to match how human vision perceives light intensity. sRGB uses a gamma of approximately 2.2.

HEX

Hexadecimal color code — six hex digits with a leading # (#FF7F50). Two digits each for red, green and blue channels, from 00 to FF. The standard notation in HTML and CSS.

HSL

Hue, Saturation, Lightness. A color model where hue is 0-360°, saturation and lightness are 0-100%. More intuitive than RGB for design work because the three properties are independent.

HSV

Hue, Saturation, Value. Similar to HSL but uses value (0 = black, 100% = pure color) instead of lightness (0 = black, 50% = pure color, 100% = white). Common in color pickers.

Hue

The "color" of a color — its position on the color wheel from 0° to 360°. Red is 0°, yellow is 60°, green is 120°, cyan is 180°, blue is 240°, magenta is 300°.

Lightness

How light or dark a color is. In HSL, 0% is black, 50% is the pure color, 100% is white.

Luminance

The intensity of light emitted or reflected. Relative luminance (used in WCAG) ranges from 0 (black) to 1 (white) after applying the sRGB gamma correction.

Monochromatic

A color scheme using one hue in multiple shades and tints. Feels unified and minimal. Common in design systems.

Munsell Color System

A color space created by Albert Munsell in the early 1900s, organizing colors by hue, value (lightness) and chroma (saturation). Still used today in some industries.

Pantone

A proprietary color matching system used in print, paint and manufacturing. Each Pantone color has a specific formula that can be reproduced exactly across media.

Pastel

A soft, light color created by mixing a pure hue with white. Pastels have high lightness and moderate saturation.

Protanopia

A type of color blindness where red cones are missing. Colors are perceived primarily in blue and yellow-green.

RGB

Red, Green, Blue. The additive color model used by screens. Each channel ranges from 0 to 255, giving over 16.7 million possible colors.

RGBA

RGB with an alpha channel for transparency. Format: rgba(255, 127, 80, 0.8) where the last value is alpha from 0 to 1.

Saturation

The intensity or vividness of a color. In HSL and HSV, 0% is gray and 100% is fully vivid. Higher saturation makes colors more vibrant.

Shade

A darker version of a color, created by adding black. Preserves hue but reduces lightness.

Split-Complementary

A color harmony using the base color plus the two neighbors of its complement (150° and 210°). Softer than pure complementary, more flexible.

sRGB

Standard RGB — the default color space for the web. All CSS colors, HTML colors and web images use sRGB unless explicitly specified otherwise.

Subtractive Color

Color created by absorbing (subtracting) light. Paint, ink and pigments are subtractive. Mixing cyan, magenta and yellow produces black in theory.

Temperature

How warm or cool a color feels. Warm colors (reds, oranges, yellows) feel energetic. Cool colors (blues, greens, purples) feel calm. Neutral colors (yellow-greens) balance both.

Tetradic

A color harmony using four colors in two complementary pairs. Typically arranged as a rectangle (0°, 90°, 180°, 270°) for balanced variety.

Tint

A lighter version of a color, created by adding white. Preserves hue but increases lightness.

Tone

A muted version of a color, created by adding gray. Preserves lightness but reduces saturation.

Triadic

A color harmony using three colors evenly spaced 120° apart on the color wheel. Vibrant yet balanced — red, yellow and blue is the classic triad.

Tritanopia

A rare type of color blindness where blue cones are missing. Colors are perceived primarily in red and green tones with reduced blue sensitivity.

Value

In HSV, the "brightness" of a color. 0% is black, 100% is fully bright. Similar to lightness but scaled differently.

WCAG

Web Content Accessibility Guidelines. The W3C standard for web accessibility. WCAG 2.2 (current) defines minimum contrast ratios: 4.5:1 for AA body text, 7:1 for AAA.

Web-Safe Colors

A legacy palette of 216 colors that displayed correctly on 8-bit (256-color) displays in the 1990s. Mostly obsolete today but still referenced occasionally.