Generally:
* Blond hair tends to be finer and have a smaller diameter than other hair colors.
* Darker hair (brown, black) tends to be thicker and have a larger diameter.
* Red hair can vary in diameter, but is often somewhere in between.
However, there are many exceptions:
* Individual variations: Even within the same hair color, there can be significant differences in hair diameter from person to person.
* Hair texture: Hair texture (straight, wavy, curly) also plays a role in perceived thickness, not just diameter.
* Hair condition: Damaged or chemically treated hair can appear thinner, even if its diameter hasn't changed.
Therefore, while there is a general trend, it's important to note that hair diameter is influenced by a combination of factors, and color is only one of them.