Final answer:
Permanent haircolor penetrates the hair cuticle and enters the cortex, the middle layer of hair responsible for its strength and color.
So, the correct answer is b) The cortex.
Step-by-step explanation:
Permanent haircolor penetrates the cuticle of the hair and enters the cortex, which is the middle layer of the hair, surrounded by the medulla (the central core) and covered by the cuticle (the outermost layer).
The cortex of the hair is composed of compressed, keratinized cells and is largely responsible for the strength and the color of the hair. This is where permanent hair dye does its work, embedding pigment deep within the hair shaft.
The permanent haircolor penetrates the cortex of the hair and enters the cuticle. The cortex is the middle layer of the hair shaft, while the cuticle is the outermost layer. The medulla, on the other hand, forms the central core of the hair.