In order to screen print a design on a t-shirt or other garment, the design must be broken down to the individual color components. The process of isolating each color is called color separation and there’s different options depending on the design and desired results…

Spot Color is used to separate colors that are not to be mixed. In this case, each spot color is represented by its own ink, which is specially mixed. When a design has very basic, solid color fills that are easy to identify, we refer to the separation type as spot color. A spot color will match specific colors in an image and will often be set to a Pantone solid color. In addition to even better coverage over dark garments, spot colors offer more consistency while printing and between print runs. Advantages: Inks can be opaque or semi-opaque / Offers best coverage and color matching on both light and dark substrates. Disadvantages: Requires the most screens for a full color image
Halftones is the technique that simulates continuous tone imagery through the use of dots, varying either in size or in spacing, thus generating a gradient like effect. The halftone process is based upon meeting the need for grays through the principle whereby a pattern small enough to be at the eye’s separation threshold will create diffusion on the retina which may convince the eye it is seeing something that is not actually there. Halftones are created through a process called dithering, in which the density and pattern of black and white dots are varied to simulate different shades of gray. Advantages: Reduces costs for photographic designs / Creates the attractive texture of typical screen printing patterns / Can be used to combine two different colors and create a third one Disadvantages: Light water base colors print on light colored fabrics only / colors might loose intensity or wash out up to 20% without proper care or after many washes and repetitive high temperature tumble dry.
4 Color Process is very useful for multi-color photographic like prints. 4 Color process is a color separation technique that combines cyan, magenta, yellow and black to reproduce the entire spectrum or gamut of colors found in the image. Process color printing usually requires more then just the 4 basic CMYK colors for a quality print. Adding a highlight white helps to control the lighter color ranges. Additional custom colors may also be included for spot color matching or out of gamut colors. Advantages: Unlimited color prints / reduces costs for multi-colored designs (5+) Disadvantages: Prints on very light colored fabrics only / cannot guarantee pantone color match
Index Color is a process where a design with lots of colors is reduced down to a limited color palette using Adobe Photoshop’s Index Color Mode. The process of “indexing” a design also converts the design to a diffusion dither random square dot (all the dots are the same size) pixel pattern rather than halftone dot patterns. The design is separated and printed directly from Photoshop, or the file is brought into a drawing program for additional text or graphic elements. You actually pick colors from within the design for Photoshop to use as your master Color Palette. It takes these colors and creates an image using just the colors you pick. All secondary colors are made using the colors you pick for your color palette.