QuestionHi! I have had downy armpit hairs since I was 11 and I still have no dark ones. I am sure you have heard what I am about to write a million times, but am I normal?
It hasn't hit a million yet, but it is well on the way.
Arm pit hair generally doesn't start to darken until late stage 3 or early stage 4 in development. You didn't mention what stage you are in, but I would suspect that you are in stage 3 -- the stage when you grow the most rapidly.
Be patient. Yes, you are normal. Development of an adult body doesn't happen overnight and some things just take time.