When a design has a low-contrast against the background color it's printed on or is going on top of visually complex background it sometimes makes sense to add a contrasting outline to the artwork to set it off from the background. This increases the contrast on low-contrast backgrounds and avoids a "camoflauge" effect on visually complex backgrounds.
See the examples below for a visualization:
Problems occur when trying to reproduce a color from a source that uses a different color gamut than then final print process utilizes.
What’s a color gamut?
Each method of producing color has it’s own range of possible colors which is called it’s Color Gamut.
Notice how none these gamuts contain the entire visible light spectrum. This is because there are certain physical limitations to the different ways of creating color.
Electronic displays create color with light which are emitted directly from a screen in the RGB gamut which is why it’s closest to the full spectrum of visible light.
Printed & painted products create color with pigments which absorb some wavelengths of light and reflect others resulting in the color you see. These colors fall within either the CMYK or PANTONE gamuts (and sometimes others) depending on the specific pigments used.
Color reproduction methods and their limitations
Colors displayed on a screen emit light directly, whereas printed colors absorb and reflect light.
Colors lighten as they combine during display
Three colors Red, Green, and Blue are emitted at varying intensities from each pixel of an electronic display, mixing to create the desired color. When each component color is at maximum white is produced. With modern display technology RGB has the largest color gamut.
Colors darken as they combine during printing
Four pigments Cyan, Magenta, Yellow, and Black get mixed through a digital printer’s nozzle while printing. When each component pigment is at maximum rich black is produced. CMYK printing has a smaller color gamut than the Spot color method, but printers that use the CMYK method are faster to set-up and can handle low-volume print runs.
Colors are pre-mixed to a particular pallet of fixed colors
Pigments are measured and mixed to produce a desired color or colors are selected from a pre-mixed set. Spot color gamuts are smaller than the RGB color gamut, but larger than the CMYK color gamut. Printing presses that use this system take time to set-up and are geared toward high-volume printing.
Computers can store graphical data in several ways. It's important for high quality print production to use the best source files in order to obtain the best results.
Two of the most common ways that images are stored are as vector and raster files. Below is a brief explaination of each:
Scalable to any size without loss of quality
Vector files store graphic data mathematically. The advantage is that your artwork can be scaled to ANY SIZE while remaining CRISP and SHARP and without losing any quality because the mathematics defining the artwork can be re-calculated PERFECTLY at any size.
Losses quality ("pixelates") when scaled
Fixed Grid of Pixels
Raster files store images as a grid of fixed pixels at one specific size. Photographs are a good example of Raster files, but many other images can be stored as rasters too. Enlarging a raster image quickly makes it "pixelated", or fuzzy, which is VERY BAD for professional print production.