So this was kind of sort of requested and is sort of something that came about after a discussion a few weeks ago about various manga coloring tutorials being hard to actually follow along with. I don't know if this is actually going to be any better, but I'm gonna try.
I've basically got two ways I color things. This way and then the actual painting with various brushes and colors and paying attention to the colors of light/reflected light/the scene way that takes like five days to do one panel. This way looks a little more flat than that way but that way leads to lots of hair tearing. So that's why this is called the quick and dirty way. It's something you can do in an hour, maybe two if you've got a large image with lots of colors. And if you're really crazy, you can do it on an already cropped 100x100 icon. Which is actually how I started doing this way because I was insane.
LET'S START SHALL WE?
You will need...
» a panel to color
» a program in which to color it. I use Photoshop CS5 but I think this is fairly translatable. You need the channels tab for image prep but for the actually coloring you should be good
» a color palette. IT MAKES LIFE A LOT EASIER IF YOU HAVE ONE OF THESE ALREADY
» optional: a tablet. It also makes life easier but it's not totally necessary
» PREPPING YOUR PANEL
» First thing you want to do is open your image in PS or whatever you're using, and then crop the panel you want. (Image)
» Next, clean it up. Usually, you'll want to trim it a little more precisely than the initial I WANT THIS PANEL cropping and there's probably some stuff in the background you're going to want to white out using the brush tool. In this image, I deleted a huge chunk of the background, just keeping Lucy, the ruins, and the foliage. (Image)
» OPTIONAL STEP: If you've got a lot of little JPG artifacts on your image around the lines, a levels adjustment layer gets rid of those pretty easily. Be careful when using this, though. It can make your black lines look all pixelated.
» The next thing you want to do is head over into the channels tab. If all you see is "Gray" you need to change your image mode to RGB color. Then you want to right-click the Blue channel and hit "Duplicate Channel." (Image)
» Create a new layer above your panel, and fill it with a light gray color. Then create a new, blank layer above that. Go to Select → Load Selection. (Image) From the drop down list labelled "Channel" select "Blue copy" and then make sure the ticky box for "Invert" is checked. THIS IS SUPER IMPORTANT. (Image)
» You'll have a giant selection fill your image. Take your bucket tool and fill the selection (while you're on your blank layer) with black. Deselect and TA-DA!! You have your lines separate from your background.
» OPTIONAL STEP: If there's anything you want the color of changed (for example, screentoned hair, or dark clothes) lock the transparency of your lines layer and then carefully color over whatever you want changed. In this image, I just made Lucy's Fairy Tail mark red.
» COLORING YOUR IMAGE
» Now it's time to color! Make a new layer beneath your lines but above the gray background and lay down some flat colors. Make sure each color gets its own layer. If you get confused as to what's on what layer, you can label them with things like "skin" or "shirt" or whatever. I'm lazy so I don't do that. (Image)
» Pick which color you want to shade first. I usually go with skin because it's the most involved out of anything. Create a new layer above your skin layer, then right-click and hit "Create Clipping Mask." (Image) This makes it so you won't color outside of what's already there on your skin layer.
» Take a color significantly darker (and more saturated) than your flat color. This is when that color palette comes in handy. Then, block in some shadows. Don't worry about this looking weird and messy, it'll get cleared up later. (Image) As for where to put your shadows, well. Look for clues like where there's hatching or blacked in shadows. Sometimes, artists will have the highlights on the eyes actually coming from where the light source is coming from. (Sadly, Hiro Mashima doesn't do this so those highlights mean nothing.) More often than not there will be something you can use as a basic guideline for where to shade.
» Make a new layer underneath your the shadows. Take a color that's lighter than your shading but still darker than your flat color and make your brush bigger and softer. I usually double the size of the brush and put the hardness down to zero. Then go in and color along the edges of where you just shaded. (Image) Sometimes I'll leave that layer like that, other times I'll go to Filters → Blur → Gaussian Blur so it blends more smoothly with the flat skin color. That's what I did here.
» Go back to the layer with the really dark shadows. Click on the blur tool and make it so the strength is somewhere between 65 and 80% and it's a small brush size. Then blur the hell out of the edges of those shadows. Some of the shadows you'll want to leave with a bit of a harder edge (like around the nose) and some of them you'll want to smooth until you can't tell where the line is and the stuff below it is. Just go with what looks and feels right. (Image)
» Highlights!! On a layer above your shadow layers, grab a very, very, very light pink or yellow and dot in some highlights. I usually do these on the nose, the bottom lip, the collarbones if they're showing, and then on the edges of the darkest shadows because of reflected light. (Image) A lot of times I'll do the highlights really small and then just leave them as-is. For this image, I actually blurred a lot of them and ended up with this: image.
» LATHER, RINSE, REPEAT for the rest of your colors. The only thing that's slightly different is hair, but I kind of suck with shading long, blonde hair so there are no images of how I usually do hair. For that, I usually start with the lighter of the two shadows and make lots of lines in the direction that the hair is flowing and then use the darker color on the same layer and blur the hell out of it. Highlights go above those. For screentoned hair, I usually pick a color much, much darker than the darkest shadows and color the lines/tones that color. (You can see how that turned out on a picture of Shanks here.)
» When you're done, it's time for some final touches. I added in a few pastel colors for the background. (Image) A lot of times I'll do a few adjustment layers to tweak the colors (Usually a Color Balance layer and/or a Selective Color layer) but for this image I just left it as is.
» THE FINAL PRODUCT
other images colored in this style: 1, 2
If there's any questions, anything I can clear up, or anything you want more example images of, let me know and I'll see what I can do. I hope this helps and y'all find it useful. c: