Coloring it all in
This part of the process is only necessary if you plan to have a full color graphic. Keep in mind that this can also be done in illustrator. I prefer to do this in Photoshop however because of the highly detailed gradients I can accomplish with it as opposed to Illustrator. If you are aiming for a more cartoonish or comic book approach, then Illustrator will work just fine.
Coloring in your graphic is very much like coloring in a coloring book. The difference is that you don't need to be so careful to stay in the lines. That's because with Illustrator or Photoshop, you have the ability to erase mistakes. Not only this, but there are some tips and tricks I use that allow me to kind of be sloppy with this. I'll share one of those with you now.
1. If you open your drawing in your art application, you can create a new layer.
2. Move this new blank layer under your drawing, and change your drawing layer to "Multiply". What this will do is allow you to see the layer beneath.
3. You begin coloring on the blank layer and you will notice that your lines stay on top. This means you can effectively go a little past the lines and the image will still appear as though you've stayed in.
I would suggest creating a new blank layer (under the drawing layer) for each color you add to the image. This will allow you to delete one color if you don't like it, without affecting the other colors. It also allows you to blur one color, lighten one color, change the blend mode of a color etc.
As you can imagine, depending on the result you want, this can be fairly time consuming. Since I was going for a more realistic approach for the face, this part of the process took about 8 hours. At this stage we are pretty close to having the graphic done and ready to add to the overall deck design. With the Joker 2.0 deck, I wanted a darker, more sinister look. A white background simply doesn't lend itself well to that. So I essentially colored the entire white background...black (which you will see in a moment).