Final answer:
The range of values of a specific color is referred to as 'value,' and when artists add black or white to adjust the shade for shading or highlighting, it creates a gradation. Hence, the correct answer is 'c) gradation.'
Step-by-step explanation:
The range of values of a specific color is called value. The term value refers to the relative lightness or darkness of a color. Artists use value to create gradation within a color, adding black or white to change its shade for purposes such as shading or highlighting in a painting. For example, a value scale can show how the addition of black creates darker values and white creates lighter values, providing artists with a range of tones to use in their work. This concept is critical in art for modeling form and creating tonal effects. It differs from contrast, which is a stark difference in colors that can bring vitality or disrupt the unity of a piece of art. Therefore, the correct answer to the question is 'c) gradation'.