Color
Visual perception resulting from the spectral composition of light reflected or emitted by a surface.
In practice
For a working designer, color is never a fixed property of an object. The same red ink looks different on glossy and uncoated paper, under daylight and warm bulbs, and on two different phone screens. Designers therefore specify color within systems, such as print inks or screen values, and check it in the real setting. A cafe menu printed in deep green may turn muddy on recycled stock, which is why a test print matters.
Often confused with Tone
Color covers hue, saturation and lightness together; tone isolates only the lightness, which is why a grayscale photo keeps its tones but loses its colors.
Try this
Place one colored paper sample on a white sheet, then on a black sheet, and note how its apparent color shifts.