not teclo its not like that the hair tends to be a lot darker outside the "head" ofc its not like light green into black But light green into dark green maybe
For one thing, maybe it's just an optical illusion, but I see the pubes in this pic as a dark green.
For another, it's easier to draw pubes in black. Other colors, you have to do the lines and then add color; with brown or black, you only need to do the lines.