Here's the sizes of natural pigment in the hair. Blue pigment is closest to the cuticle layers in the Cortex , then the red pigment is next deeper into the Cortex, followed by the Yellow which is deep within the middle near the medulla.
Melanosomes Melanocytes Melanin
Cross section of the hair showing dark triangular hair mixed together with blond smaller round hair. On the bottom right there is even a white hair!
Blonde hair, some have a medulla and some do not.
You can actually see where the hairs pigment is coming from and how it moves up the hairshaft