Technuque 1)>Cel shade
Whether a line is or isn't separating the shades doesn't matter . In fact this is truer to classic traditional cel shading, They often had the separating lines in a different color than the shade. I'm unsure as to why this was a practice. My best guess is when they did the lines on the front of the cel with the paper behind as reference, they would mark the shaded areas with an arbitrary color to save time and add accuracy to the coloring. THis way they wouldn't need the paper twice, and would only need one pass for the colors.http://i.ebayimg.com/images/i/162221337207-0-1/s-l1000.jpg
These bright accents, especially of the bluish pinkish spectrum, are there to give the piece an iridescent lookhttps://en.wikipedia.org/wiki/Iridescence
skin and clothing are (for the most part) not iridescent by nature
This is a hunch, but it seems that what these colors achieve is a sense of very bright lighting and atmosphere, even without a background or any glows.(exceptions: slight airbrush on the highlights on her thighs and pants' inside as well as on her tit highlight,jacket, the shaded area dividing her stomach, and the blush)
Technique 3)>Mixed media
Traditional sketch painted digitally.
You can see the pencil lines very prominently in the hair.
Instead of painting over them they incorporated them into the drawing and drew in the same layer. I'm assuming part of this workflow is assisted by the csp bucket, although it's not crucial to getting this look.
I don't do iridescence often, but most of my work is cel shade and digital ink and paint.
I don't usually like these kinds of threads but this is an exception for being something I'm curios about myself.