"No background" is called a transparent background. There's nothing there, so it takes on the color of the DA page. You'll need an art program that supports transparency, such as Photoshop, PaintToolSAI, or Manga Studio. You just draw your character, and don't fill in the background. In some programs you'll need to hide the "background layer", which causes a grey and white checkerboard to appear. Regardless of the art program, you'll need to save the picture as a .png to preserve that transparent layer.Hope that helps