For those that don't know, flats are what a colorist uses to select different parts of the art without affecting others. Although this is a very tedious part of coloring, it saves you a huge headache later on, as we'll see. Sometimes when working with a larger publisher or team, you might receive the pages with the flats already done, but since that isn't always the case, let's work on that too.
Normally all the flats are done in one layer (the background layer for example), but since we're going to be creating the background, it's best if we put the characters on one layer and the background on another. This is done easily - in the layers window, press the "new layer" button found at the bottom of the window. This will create a new layer; let's call that layer "flats-characters". Now double-click on the background layer, click ok and rename it "flats-background".
Make sure the "flats-characters" layer is selected before continuing to the next step.
Now we start laying the flats using the Polygon Lasso tool, which can found in the tools menu (Fig.07). Select the tool, zoom into your line art and start selecting along the lines. Be careful not to select outside the lines; it will make it all look messy further on. And make sure the settings in the sub-menu are as shown in Fig.08.
The process is simple: click along the lines until you have the object you want to fill selected and then fill it with the paint bucket tool.
A quick word about the way I prefer to do my flats. I pick the color that's going to be used most on the character and fill in my whole character with that color, as seen in Fig.09. This way, when I want to add the other colors, I can select more loosely. If I select a boot very tightly along the leg, for example, and then select part of the background, when I click with the bucket on the boot, only the parts with the same color will fill with the new color - the background won't be affected. This can be used with all your flats.
Now, use the same technique to lay down all your flats on the characters and then do the same on the background layer until you have something similar to what I have here. It doesn't really matter what colors you use here, because you change them at any time (Fig.10).
Part 2 : Creating The Background
So you've got your line art prepared and your flats are laid down... where to go from here? What I generally like to do, is finish off the background first. That way I define all the light sources and colors that will influence the page.
In this piece the artist has left us without any concrete background and I thought that instead of just adding a gradient or simple background, we could create a background. And what better background then some storm clouds (because of Storm of course!)
So to start, let's turn off the character flats layer and the line art, which basically leaves us with the background flats (Fig.11).
Creating The Lightning
Ok, so let's start with some great lightning! Create a new layer above the flats layer by pressing the "new layer" button. Call this layer "Lightning". (To change the name, remember to just double-click on the name in the layers window) (Fig.12).
Select only the lighting by going to your flats layer and using the Magic Wand tool with the settings shown in Fig.13.