It is unclear what caramel hair is. However, the color caramel
is a color many woman like to have in their hair. Many companies
make hair dye that can change the color of a woman's hair to the
caramel color.
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caramel
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Caramel is thermally decomposed by heating.
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It can be, at least for the yellow-brown color of caramel (burnt
sugar).
Other uses of caramel are a noun, or a noun adjunct (caramel
apple, caramel candy).