Here's why:
* Hair Color Spectrum: Hair color is determined by the amount and type of melanin (pigment) present in the hair shaft. Black hair has the highest concentration of eumelanin, while brown hair has a mix of eumelanin and pheomelanin.
* Variations: There is a wide spectrum of brown hair colors, ranging from light brown to almost black.
* Lighting: Even within a single hair strand, melanin distribution can be uneven. This can make hair appear darker in some lighting conditions and lighter in others.
Therefore, "blackish brown" is a valid description for hair that falls somewhere between black and brown on the color spectrum.