Spot and Process Colors

You can create and manage custom colors by choosing Edit > Colors on the main Scribus menu bar, which brings up the Colors dialog (see Figure 7-28).

Figure 7-28. Scribus comes complete with predefined colors, using names of its own.

Note that most of the ready-made color names, like AliceBlue and Burlywood, have a small icon with red, green, and blue stripes. This denotes that these shades are defined as red, green, and blue (RGB) colors, which are useful for web design, video work, and PDFs destined to be read on screen, but not so useful for matching colors on a printing press.

Because mixing ink to make a particular color is the opposite of mixing light on your computer screen, instead of RGB, color printing typically uses the direct opposite primary colors of cyan, magenta, and yellow (CMY); see Figure 7-29. In practice, it can be tricky to mix black accurately from these three primary ink colors, so most color printing is done with an additional key color of pure black ink. The letter K, for key, is added to the acronym CMY to make CMYK. Other color models used in commercial printing presses use six or more inks, plus varnishes and other translucent finishes; but CMYK is the most common model in the world of DTP.

Figure 7-29. Subtractive mixing of colors with cyan, magenta, and yellow light absorbers. Note the red, green and blue parts where the colored glass filters cross over. 3D image modeled in POV-Ray by Mirsad Todorovac, GNU FDL.

If you've ever opened a cereal box and wondered about the cryptic symbols printed on the inside flaps, they're alignment and color proofing marks from litho printing. The offset litho technique can print only one color at a time, using a metal plate that transfers the ink onto a roller; then, the roller puts the ink onto the paper. A full-color image therefore requires at least three different inks for the primary colors plus key ink, which means a minimum of four different plates and four runs through the press.

Registration marks, which are on every plate and look like cross hairs, help the printer make sure each subsequent color is printed exactly on top of the color before. If the paper in the litho machine or the printing plate is even slightly misaligned between runs, you see colored fringes around the edges of an image; you may have noticed this common error in a newspaper or a comic book, if you have a keen eye. Cropping marks, which show the print finisher where to line up the paper cutting machine, are often printed using the registration color.

Sometimes you can get away with black ink and one other color, which means the printing press runs only twice, making the litho job cheaper. For example, if you're printing stationery for a company that has only black text and a logo that is always the same shade of green, there's no need to use three different color plates as well as the black plate. These specific colors are known as spot colors, and they're usually specified by designers using the proprietary Pantone system of color swatch numbers. That swatch number translates into ratios of basic ink colors so that the printer can mix up a batch of ink for that one job.

Mixing inks for litho is a lot like what you do when you're painting a house—you take the paint company color chart to the hardware store, and they have a machine that adds precise amounts of pigment to a can of ordinary white paint. It saves the printer or hardware store from having to keep vast numbers of different spot colors ready mixed, which they may never need. Printers also use spot colors for inks that can't be mixed using CMYK ratios, such as metallic and fluorescent finishes.

Scribus doesn't support Pantone numbers by default, because their proprietary nature is difficult to reconcile with Free Software—not least because the owners of the Pantone system require license fees to be paid before you can reproduce or distribute their swatches. Instead, you can use the New button in the Colours dialog to open an Edit Colour dialog where you can specify a CMYK color by the percentages of the four inks (see Figure 7-30). To help you mix colors by eye, Scribus provides a hue, saturation, value (HSV) color map, similar to the GIMP's color picker. The drop-down menu at upper right lists the predefined swatch values you saw earlier.

Figure 7-30. Choose a color model, and then specify the percentages of each primary color plus black in the case ofCMYK.

Choose a memorable name for your new color; select the color model from CMYK, RGB, or the very limited web-safe RGB palette; and click the check box for spot color or registration color if appropriate. Then, click OK to close the Edit Color dialog. Back in the main Colors dialog, your new color is displayed; if it's a CMYK color, it has a different icon than the ready-made RGB colors (see Figure 7-31). Click OK again to close this dialog, and you can use your new custom color in the Edit > Paragraph Styles dialog.

Figure 7-31. After creating a new color and giving it a name, you're no longer limited to the ready-made swatches distributed with Scribus.

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