Hair color change and hair growing back thicker

After I shaved my head a number of years back my hair grew back light brown instead of my normal blonde. Does anyone know why this would happen? I have heard that hair can turn dark due to toxins, but I was wondering if it could be genetic. I know it's popular on CureZone to attribute things to toxins, but I don't think the genetic component should always be disregarded. The same thing happened to my Dad as happened to me (at around the same age), although his hair turned dark brown. My grandmother once told me that my hair would turn dark when I was older because I had dark eyebrows. I have no idea if there was any basis to this statement or whether she was just being priggish.
Also, I have read different things about shaving hair. I have hirsutism, with a few dark hairs on my chin from that, and people on CureZone seem to have different opinions on whether shaving hair will make it grow back thicker or not. I have read on other internet sites that this is just a myth. Does anyone have an opinion on this? Tweet