Now you are going to set up your file to color.
1. Select all(Command-V).

2. Copy (Command-C).

3. Make sure on your color choice that black is over white. The two squares at the bottom of your tool palette.

4. Delete it. Your image will disappear, don't worry.

5. Now you must change your image to "GRAYSCALE" then to "RGB".

6. Go to your "LAYERS" palette and open the "CHANNELS" dialog box. Open the sub-menu and hit "NEW CHANNEL". A dialog box will appear. Click on the color box that is shown. Change whatever color it is to BLACK there is box labeled OPACITY. Make sure that is set at 100%, hit OK. Your file will turn black, don't freak.
Your dialog box and settings should look similar to this.

7. Paste your image into the new channel(Command-V). Your line art will appear as normal in your newly created color channel.

One last bit before we go on: The eye icon next to each channel shows that they are all visible. But the 'RGB' channels are the selected channels, that way we don't draw on top of our line art. Make sure before you start flattening that you are drawing in the RGB channels not the Alpha!

At this point I suggest on buying a WACOM drawing tablet. This works like a pen drawing on paper opposed to the mouse. It's almost impossible to carry out the next steps with a mouse, unless you have a lot of time on your hands(which if you work in comics you do NOT!).

8. Now you can "flat" your page. Choosing your pencil tool, outline the inner portions of each element of your artwork. Ex; flesh, shirts, pants, hair etc. Making sure you connect your lines, fill in the middle with your paint bucket tool. Kinda like a coloring book when you where a kid. Make sure each element is in a different color. You will notice you are working behind your line art. Stay within the lines. Bleeding under the line art is good but try not to go outside the lines, nobody likes a sloppy colorist.

9. It takes a while to get used to the drawing tablet. The more you use it the more comfortable you will get. I suggest you don't use your mouse and start to use the tablet for any other tasks you do on your computer.

10. After flattening out the whole page you can put them in channels. Taking your magic wand tool select all the elements that go together. Ex; select all the flesh, faces, hands, legs etc. Then put them in a channel by clicking the "Save Selection As Channel" button at the bottom of your Channels palette. Now repeat with other elements: shirts, shoes etc and put them in another channel. Don't select elements that butt up against each other. Ex; a face and the shirt. The reason for all this is after you're done rendering your piece you can select the channel and tweak it to your liking by colorizing it or saturate or desaturate it. If you think the flesh is too pink, you select your flesh channel and tweak it. Instead of using your lasso tool and redrawing around all the flesh elements. So now our Channels Palette looks like this.

11. After you're done putting all your elements in channels your ready to render!