I have brown hair which is the second most common hair color.
Mine is more dirty blond - I wish it were either darker or lighter LOL!  And who came up with the term dirty blond, sounds well dirty LOL!
Brown hair strands are thicker than blonde but red hair strands are the thickest. 
I had no idea that the strands of different colored hair vary in thickness - I wonder why that is, do you know?
I have no idea but thought it was interesting as well
It is - I wonder if it changes when the hair is dyed - or only if that's your natural color.  I've tried to dye mine red before but red hair dye fades super fast.
People call brown hair brunettes which comes from the french word brun.