A "shadow condition" is the stuff that Brian Haberlin is famous for...he makes the shadow areas of things look even deeper in
depth and richer in texture than how most colorists work it. He taught the Top Cow people this method too, and you can tell in their coloring.
Notice how the darkest part of her skin (the shadow on her neck, the outside parts of her jaw, the inside corners of her eyes) are a warm peachy-red-brown tone? A "shadow condition" would be to cool off those areas so they look a little darker, a lot less saturated, and a bit bluer than standard flesh tone. Cool, de-saturated colors recede; this makes the warm colors pop more. So if I were to render this piece now, I'd have a lot more than just skin tone on Ivana's face.
The orange arrow points to an example of shadow conditioning. Where the shadow of the upper lib falls, where no other established light source reaches, is where the shadow is the darkest. Putting a cool color in here (blue, for instance) makes that area more dynamic.
I always start out with a dark Base Tone and work up to the lightest or brightest point. (In the case of the gums and teeth, since they are shiny, my highlight is white). Then I go back into the shadow areas and do the secondary lights and/or shadow conditions.
Remember: These colors, percents and results are not set in stone! Screen is tricky and it takes practice to be able to predict the results. Practice, with your own colors and see what happens.
This is how I would do Ivana's face with shadow conditions. I added some de-saturated blue/purple to the cast shadows on her forehead and neck, to her nose, chon, eyelids, and around her shoulders. You can see how much more realistic and dynamic her skin is now. I used a combination of Multiply, Normal and Color to create this effect.
More information on these terms as well as other ways to get pages covered in Photoshop in the tutorials ahead. For now, just practice with every little inked picture you can find and you'll slowly learn more and more about coloring. Also observe the colors, shadows and highlights of the things around you.