Viewing Color on Your Monitor.  One of the most important things to realize when ordering work from an online printing service is that there is a distinction between the image you view on your computer monitor and the image that will ultimately be printed on a printing press.

Computer monitors use RGB to display color. RBG stands for Red, Green and Blue. When you print something to the CMYK process, for best results, you need to convert any RBG images to CMYK images first. Sometimes you’ll see some changes to the image when you make this conversion, so it’s better that you see the changes first before uploading your file.

Also some colors that you see on your screen are very difficult to reproduce exactly using CMYK (or any other printing method). Therefore if you have the software that enables you to process your image into CMYK before you upload the image to the printing service, you’ll have a close idea of what you’ll get once the printed products are shipped to you. Some of the hardest colors to match going from RGB to CMYK are blues. 

You also have to take into consideration that different monitor types display colors differently. For instance, many LCD or laptop monitors cannot display as much of a range of colors as other monitors. On these monitors, colors can lose contrast and many colors sometimes look similar to others (for instance, dark greens and browns).

Professional designers and prepress companies use color-calibrated monitors to ensure that the color they see on their screens is as close as possible to the actual color of the file. Most home users cannot afford to purchase these very high-end monitors, and therefore have to understand that there will ALWAYS be variance from what they see on the screen to what they see on their printer, or any other output device.

CMYK Printing.  CMYK stand for Cyan, Magenta, Yellow and "Key" (black).  CMYK printing can reproduce most color photographs very well. In traditional printing, a full color photograph is scanned and then run through software to create 'color separations.' Once the separations are processed, and 'plates' are made for each of the CMYK colors, the printer runs the ink through the plates on press, and the result is your full color image printed on paper.

CMYK is the most economical method of reproducing full color images in the highest quality, and most magazines and glossy collateral is printed using CMYK. CMYK is the standard method that most printing services currently use to process print jobs.

Other Factors Influencing Printed Color.  Most home and small business printers are either inexpensive ink-jet printers, or color laser printers. It is impossible to calibrate any of these systems as they have a wide and varied range of methods of printing. Even though some printers use CMYK inks, many other factors have to be considered, and it is impossible to expect to consistently print perfect color.

There are many possible factors that can affect the color on your printed materials. The weather outside can play a part in affecting how the ink dries on the paper, and can change the color slightly. The paper delivered from the paper mill may be slightly brighter. The ink density and constant on-press fluctuations in color, printing press running temperature or blanket wear, could also affect color slightly. It is impossible to expect that any professional printer can produce exactly the same printed blue on two separate days.

Recommended Process Colors.  These settings are recommend for black, white, and blues:

Black (text, image, background, etc.) should be 100% Black, (C:0, M:0, Y:0, K:100) 
White (text, image, background, etc) should be pure White. (C:0, M:0, Y:0, K:0) 
Blue - In the Four-Color Process, some blues that look blue on the computer screen tend to print purple. Also, the lighter the blue, the more purple it gets. For example, a blue gradient that starts with a deep blue will more than likely start to turn purple as it gets lighter. Here are some safe process blue colors:

192-1, 196-1 to 227-1 
197-2 to 227-2 
214-3 to 227-3 
211-4 to 227-4 
211-5 to 227-5 
211-6 to 213-6, 218-6 to 227-6 
211-7 to 213-7, 218-7 to 227-7 
211-8 to 213-8, 218-8 to 227-8 
211-9 to 213-9, 218-9 to 227-9