Oh that glow! Yeah, I did that by some careful layering. All of my skin tones are 3-5 layers of color, sometimes more or less depending on what kind of effect I'm going for. For Koreal there, I colored his skin in with a very pale peachy color that I knew wouldn't scan very well, and used an also very pale blue-green for the places where the glow from the book would hit, and very carefully feathered the blue into the peach using light upward strokes that barely touched the page, and then smoothed the edge by going over it with the peach again. Then I colored the non-glowing portions of his face with the rest of its usual colors (light/med/dark peach, and 2-3 layers of a blue-grey shadow color).
You really have to move quick for this, and it can help if your markers have different amounts of ink in them (the peach was pretty juicy, which helps it lay down smooth and blend, and the blue was a little bit dry which kept it from depositing TOO much ink). It may also take some time to figure out which colors blend well with each other... and which don't.
On top of that, it helps to know which colors scan well and which don't-- and sometimes you can use that to your advantage, because sometimes the ones that don't scan well look awful by themselves... but sometimes the fact that they don't scan actually helps a glowy effect.
(God I hope that all made sense. Someday I'm going to have to just film myself doing this stuff, because explaining it is so hard...)
... Based on my own process (see above), I'd say you absolutely can put many layers on your markers if you know what you're doing, but my way absolutely doesn't work for everyone because it is labor intensive, easy to do poorly, and quite frankly relies on having a LOT of colors, which gets hella expensive.
