Be curious to know what he is using if you can find it. My guess he is using Faber Castell Pitt Artist Pens. It seems that most are using either those or the Copic.
Never tried the Faber Castell, but I think
@Steve in VA uses those??
I picked the Copic as those are what Bill Boehm (on the AAW Forum) was using and recommended for his basket illusion pieces. For me, I chose them for three reasons. 1. They are refillable so you aren't buying more pens. 2. They have replaceable very fine nibs that you can shape to suit your needs and color all the way down the side of a bead without coloring adjacent beads, and 3. They are dual ended with a large tip on one end that can be used when coloring multiple adjacent beads.
I don't know that one is better than the other, I picked the Copic as Bill had been using them for several years and liked their performance for that use.
The one downside is this model of Copic pens (Copic Original) is not carried in most hobby stores. This doesn't matter much to me as Dick Blick carries them, and their headquarters (and retail store) is only 15 miles away.
Nevertheless, I've always planned on picking up some Faber Castell pens to try, just never got around to it.