NOTE: I’m not going to try to create an entire glossary here. Instead, when a client asks me what a word or phrase means, I’ll post it here (after I answer them, natch.)

Color

The visual sensation dependent on the reflection or absorption of light from a given surface. The three characteristics of colors are hue, intensity, and value.

See the NBS/ISCC Color System for a good education in how to talk about colors. There is another version here. Aubrey Jaffer has a very thorough listing and discussion of various color libraries and systems here. (warning: heavyish science content)

Contrast

The degree of difference between the lightest and darkest parts of a picture. Or differences between two or more elements in a picture. (e.g., value, color, texture.)

Hue

The name of a color (e.g., red, blue, yellow, orange).

Highlights

The lightest values in a picture other than the Specular Highlight. Highlights are usually the color of the light in the scene rather than the color of the object on which the light is falling.

Intensity

Also called chroma or saturation. It refers to the brightness of a color (a color is full in intensity only when pure and unmixed). Color intensity can be changed by adding black, white, gray, or an opposite color on the color wheel.

Midtones

Brightness values near 50% gray, or a range of tones between the Shadows and the Highlights.

Saturation

Also called chroma or purity. The intensity of a specific hue. A highly saturated hue has a vivid, intense color, while a less saturated hue appears more muted and grey. With no saturation at all, the hue becomes a shade of grey.

Shadows

The darkest values in a picture. Shadows are usually the color of the reflected light in the scene rather than the color of the object on which the light is falling. (e.g. blue shadows in an outdoor scene under a blue sky.

Shadow Point

The point beyond which all darker pixels will print (or appear onscreen) as black.

Specular Highlight

Highlight area with no printable information, thus no detail, as compared to a diffuse highlight. Also called catchlight and dropout highlight.

Value

Lightness or darkness of a hue or neutral color.