Final answer:
Three primary colors are necessary to produce a natural-looking hair color when dyeing: red, yellow, and blue. The correct answer is 3.
Step-by-step explanation:
To produce a hair color that looks natural, three primary colors must be present: red, yellow, and blue. These are the foundational colors that can be mixed in various ratios to achieve different natural hair colors when it comes to hair dye.
Permanent hair coloring typically involves a process that includes hair dye components that react during the dyeing process, often involving a compound called a coupler, which defines the specific color outcome. Different couplers can give shades of red, yellow-green, and blue, which then mix to create a spectrum of natural-looking hair colors. Hence, the correct option is 3.