VOCABULARY : Additive mixture principles apply to how colored lights combine. Afterimage is a visual sensation that occurs after one stares at a color for some time. The visual stimulation of any hue in the retina will bring up a reaction to its opposite. Chroma is the degree to which color is mixed with white (tinted), black (shaded), or gray (toned). It is often used interchangeably with saturation and intensity. Chromaticity is a property of the color of an object or light that does not depend on brightness. It is defined in terms of the major light wavelength present (hue) and the saturation (the degree to which hue is mixed with white or gray). Color, often used interchangeably with hue, is a property of light and is defined by its wavelength. Primary colors are those that can be used to make other colors but cannot be formed from a mixture themselves. Secondary colors are half-steps between two primary colors. Tertiary colors are half-steps between two secondary colors. Complementary colors are colors directly opposite each other on the color wheel. Complements neutralize each other in mixtures and accentuate each other in juxtaposition. Color bias is the color undertone. It can be seen readily when the color is brushed lightly against a white surface. Use the color bias to determine whether a color is warm or cool. The most intense mixtures can be obtained with colors biased towards each other. Color wheel is the simplest and the best system for showing color relationships and color interactions. Isaac Newton first proposed it by bringing the ends of the color spectrum together to form a circle. Though there are other color models, the color wheel is the most useful for painters. It is based on the primary colors, has equal visual steps between colors, and its colors are more consistent and predictive in their mixtures. Constancy effect is where the mind determines the color rather than the eyes; because we know a handkerchief is white, we see it as white whether it is in strong sunlight or a dimly lit room. Hue is the wavelength of a color. It is often used to refer to the colors of the rainbow; it can also refer to a shade, a complexion or an aspect of color. Inherent value is the value of the pigment itself; for example, yellow is lighter in value than blue. Intensity is saturation of a hue, i.e. the color's distance from neutral gray. It is often used interchangeably with chroma and saturation. A weak hue is almost neutral gray; a strong hue approaches the intensity of a spectral hue. The most intense mixtures can be obtained with colors biased towards each other. Cool colors mixed together, or warm colors mixed together give greater intensity than mixtures of cool and warm colors. Iridescence is the quality of shimmer and changeability of a color. Iridescent colors have the same value and intensity. Luster is reflected light, sheen, a glow of light as if from within. For an object to appear lustrous, a dark contrast or background is required. Luminance is light radiating or reflected from a surface. The creation of luminosity requires subtlety the choice of color and in the composition. For examples of brilliant lighting effect, look at works of Titian and Rembrandt. Mixtures: Color pigment differs from color in light by its subtractive quality. The mixing of color pigments is a subtractive process. For example, red pigment reflects only the red area of the color spectrum, while absorbing all other wavelengths; when green pigment is added, the mixture has a combined subtractive effect where most wavelengths are absorbed, including the red and green wavelengths, resulting in the reflection of a neutral color. When two colors are placed side by side, the subtractive effect can enhance or subdue each one. Neutral color is the mixture of a color with its complement; it has little or no decided color. Neutral gray is a combination of black and white. Opacity refers to the degree which light is prevented from passing through an object. Optical afterimage is a phenomenon that occurs when one stares at a saturated hue for a long time then glances at a white area; the complement of the hue will appear briefly. Partitive mixture is an optical mixture in which the eye will blend small bits of color. The pointillists used this technique. Saturation, often used interchangeably with chroma and intensity, refers to the relative purity of color. The primary colors are fully saturated; they are "pure colors." Semi-neutral refers to colors mixed with white (tinted) and colors mixed with black (shaded). Shade is color mixed with black. Brown and navy are colors mixed with black. Temperature refers to the warmness or coolness of a color. Cool colors are receding colors (green, blue, violet). Warm colors are aggressive colors and tend to approach (red, orange, yellow). Tint is color mixed with white. Pink and lavender are mixtures of pure colors and white. Tinting strength refers to the amount of color required to tint with white; for example, only a little alizarin crimson is needed, while a lot of yellow ochre is needed to tint white. Tone is the relative lightness or darkness of a color; it is color mixed with black and white (grayed). Rose and beige are pure colors mixed with white and black. Transparency refers to the degree color allows light to pass through it and reflect back from the color beneath. This technique is used in atmospheric perspectives. Transpose means to change in form or nature, or to change the relative position or normal order. Undertone: see color bias. Value is the relative lightness or darkness of a color. All colors have inherent values, for example, lemon yellow is light in value, whereas indigo is dark in value. Each color can be varied in value (tone, tint, and shade). A photographer's gray card shows a gradation of white to black. Middle gray can be determined by looking at the border value between white and black.