Which of the following is NOT one of the four classifications of hair coloring products?

The classification of hair coloring products typically includes semipermanent, demipermanent, and permanent colors. Each of these types serves a different purpose in hair coloring.

Semipermanent color is designed to last for several weeks and gradually washes out, while demipermanent color uses a low level of ammonia or none at all and typically lasts longer than semipermanent. Permanent hair color, on the other hand, provides the longest-lasting results as it penetrates the hair shaft and changes the hair's color until it grows out or is cut.

While "nonpermanent" might seem like a possible classification, it is not commonly recognized as one of the established types used in professional hair coloring. Instead, it may refer to semi and demipermanent variations, which indicates that it doesn't exist independently in standardized terminology. This distinction solidifies why the correct answer is that "nonpermanent" is not officially one of the four classifications of hair coloring products.