[the following is a copy of an email I wrote in response to a question about digital coloring]
Don't feel bad if your teachers don't have a lot of technical advice on working digitally. All I did in college was paint in acrylic and oil, and it was the same for buddies of mine like Josh Cochran, Sam Weber, Jillian Tamaki, Tomer Hanuka, and James Jean. Also, I teach at a great school in Baltimore, and I don't let most of them even touch the computer.
The way I learned digital coloring was pretty straightforward: trial and error. Basically, I wanted my work to look like it was a printed comic book page. Everything else slowly evolved out of that.
Early on, I hated the "slickness" of digital coloring, having been a very textural painter in school, so that was a big part of the learning process. One option for getting a bit of texture into the image is to scan it so that you have some paper texture with the line work.
Another option you may want to try is to scan in some papers you like. I have 4 or 5 that I go back to, depending on the assignment, such as newsprint, etching paper, and watercolor paper. You can use "Multiply" to have them add texture to your artwork. It will take some fussing around with until you get it how you like it.
I also like to experiment a lot with my illustration process. Most of the time, I will make unique textures for each illustration and scan them in separately. If you have a printer, you can print out your ink work in a light color, and then try doing ink washes over it for shadows & stuff.
And for keeping your lines black, there are several ways to do it, but the "multiply" option is the easiest.
All that said, I'm going to reiterate the point that you don't need digital instruction in school. It's much more important for you to focus on design and composition. Know how to use the computer, but don't use it for making art from scratch.
If you look around the web and notice that your work fits in too much -- that is, if it looks a lot like what everyone else is doing or like what everyone else is trying to do -- it's a very bad thing for your future career. Do whatever you can to stand out. I worry about all the digital artists coming out of school these days -- not for myself, but for them, because they all look the same.
My work is going to start looking very dated in a few years, probably... which will be bad for me, but much worse for new artists who are just emerging and already look dated. So, I advise playing around and trying different media for a while. It's easier to learn watercolor or acrylics while you're in school than it is when you're trying to pay rent. Or, you could try tweaking your drawing style-- anything to make you stand out from the pack. Find out what is unique or weird about your own sensibilities.
As fashion metaphors are concerned, it's better to dress like a techno-goth weirdo, than to look like 90% of the population who just walked out of the Gap.
I checked out the link you gave me, and it seems like you know about as much as you need to know for digital coloring. There's really no magic to any of it, just play around with layer settings like multiply, color, overlay, and opacity, and see what comes of it. Work on your drawing and design skills.