Spot Color, Process Color, and the Color Bridge

Let's tackle the single most misunderstood area in all of printing terminology. Let's see if we can get our minds around the different ways color is handled in a printshop. After this, let's go have a cup of coffee, because I am BEAT from making all these graphics. (Speaking of the graphics, click on any of them for a full size version.)

Here is the important part. I realize it will be impossible to learn from this post everything you need to know about color issues. What you can do, however, is understand enough to have an intelligent conversation with your print vendor(s) before you begin detailed work on your layout. The situation we must avoid is that your file goes through the entire layout process in CMYK, (or RGB, God forbid) and then it turns out that spot color printing is the compelling choice. It is often a huge amount of work to "retrofit" a CMYK file into spot colors. (The reverse, on the other hand, is easy.) This is a common trap that designers fall into if their primary focus is web based graphics, and their program of choice is Photoshop.

"SPOT" Colors: The most simple color model is the spot color, where we make one plate to print one color. Each plate we make incurs a cost, so the lowest price job is one "spot" color. There is no "wash-up" charge to print black, so it's the cheapest of the cheap.


Spot colors are mixed according to guides published by Pantone, Inc., and have designations such as "Pantone 186 C," (where the "C" refers to a color shown on a coated stock, see here for more). These colors are mixed much like paint at Benjamin Moore...component mixing colors are weighed out in precise amounts and the whole mass is blended into a single color. You can think of the plate which applies the ink in a similar way because, like a paintbrush, it can be "dunked" into any color you want to put into the ink tray on the press.

By this reasoning, the exact same plate image above could be mounted on the same press with blue ink in the tray and the result is below (Good Dog, Sammie!):


The addition of a second color seems like it would be simple, but, often, it's not. You must be sure your file and all linked graphics are capable of separating into the colors you have defined, and only those colors. Raster based graphics (ie. from Photoshop) are most often incapable of performing this seemingly simple trick, unless you know a lot about channels. Regular, run of the mill JPEGs just won't do it. Beware.


If you want to verify your file will behave in this fashion, "print" it to Adobe PDF writer and specify "separations" as the output mode. For a two color job, the resulting PDF will have image on only two pages, etc. (You may get CMYK pages as well, but they should be blank.)

I will make you a bet right here...the first time you try this, you will end up with image on extra pages because something in your file will have a CMYK piece or part. No joke, I'll actually buy you lunch if I'm wrong. We fix files ALL DAY LONG that have extra colors, and it costs time and money.

Process Colors: are defined from multiple sources but are all encoded the same way...as percent values of the four "process" colors Cyan, Magenta, Yellow, and Black (CMYK). They can be stored as the color values within a digital image, defined (again by Pantone, Inc.) as CMYK equivalents of the Pantone Solid (Spot) colors, or translated on the fly from the native RGB colors which drive many digital devices. (The latter is the instance which often causes problems which I referred to as "Lost in translation".) Regardless of how they get in the file, however, they always come the same way...four distinct images, one for each of the four process colors:


Why spot colors? The chief advantage of process color, the ability to reproduce photographs or other full color graphics, is so easy to understand let's look instead at the unique ability of spot colors. The main advantage is a question of Gamut, or the range of colors which may be achieved with a certain color system. Look at the following graphic and imagine getting this selection in a box of crayons:


Now imagine your box of crayons contains the Spot Color palette below, and the effect it would have on your ability to precisely blend colors...the "Gamut" is obviously much larger:


The Color Bridge is the intersection of these two color models, and is the one indispensable product you must own from Pantone. Each page shows a column of Pantone Solid (spot) colors on the left, and the best CMYK blend that can be achieved to replicate the same color on the right.


This guide (available here) is where you MUST look when you are choosing colors to build into your layout because it shows the colors as they will actually be printed. It allows you to know with certainty how the colors will print regardless of how they appear on your monitor or inkjet prints. Most important, if you have established a Pantone Solid (spot) color as part of your identity or layout, and consider switching to CMYK, this guide will alert you to a possible problem if the color doesn't render well in the new color model. Remember, the CMYK gamut is much smaller...not every spot color has a good CMYK match, and some are actually terrible. Beware.

Digital printing mixes it up. It used to be simple to determine the choice of spot vs process because, in a conventional offset environment, the cost of four process plates vs., say, two for a two color job, was decidedly higher. In today's mixed offset/digital print shop the distinction isn't so clear and the Color Bridge question is especially important. It may be that a CMYK digital device can render a small quantity of a two color job, converted to Process Color, less expensively than actually making two plates. The decision will depend on the quantity, (digital machines favor short runs) and the resulting quality of the Process Color that results from your file on that particular device. (All digital printers are CMYK and the colors vary a LOT from machine to machine. Insist on a proof copy.) In a longer run, (over 1,000) offset production with conventional plates, in either color model (offset presses can run either, or even both at once!) will start to look attractive.

The important part, again. Use this information to have an informed discussion with your print vendor as you begin serious work on your layout. In addition to cost, be sure to discuss consistency between this project and other collateral material which may have already been printed with specific colors. Be sure you understand, in detail, what colors you've chosen and how they will appear when printed via the most economical and quality-appropriate method. Then be sure your file is capable of rendering those colors and only those colors. It's both as simple and as complicated as that.

As always, I look forward to any questions or comments you have. Until then, see you online!

Hugh Butler
Your friend in the printing business