If you are preparing your digital files for commercial printing of a 4 color (full color) order, make sure when designing your files that you are using true 100% black for your any black text that you are including in your design. When printing in full color, consider that there are four color plates needed for printing which are referred to as CMYK or Cyan Magenta Yellow and K = Black.
Doing so will provide you with sharp and clear text throughout your full color print, here's how it works:
Most all publishing programs including Adobe photoshop, illustrator, quark, indesign and publisher allow you to control the specific color information of your text as compared to the other full color images in your artwork. Consider that all imagery including text is created from a series of 4 color plates as described above, CMYK. Unless you specify that the text in your artwork uses only 100% K (black ink), then what looks like black ink is really a combination of all 4 colors, giving your text that appears black but is not really a pure solid black, and can look blurry as compared to pure black text.2) The difference between one color 100% black and four color black text and how printing registration matter.
The problem with designing artwork with four color text lies in understanding how a commercial offset press work. Offset presses are equipped with four print heads each containing specific color of ink. For example, on a four color press, the first print head contains Cyan ink, the second contains Magenta ink, the third contains Yellow ink and the last print head contains Black ink.
When we receive your files we need to "rip" those files which produces four color negative plates, one plate for each color. In reality we are digitally separating your file into these plates to setup for the offset printing process. Once we affix your plates to the print heads each with it's own color, we then align the plates and begin printing your job. If you have four color black text in your file, then each color plate will contain a percentage of color to print on paper which is where the problem lies.
Think about how difficult is can be especially with smaller type to send thousands of sheets of paper through 4 print heads while keeping every plate aligned in perfect registration for each letter in every word. If only one plate, (the black plate) contained the color information to print your text, then there is no problem because the text printing is actually being produced from one black plate and not a combination of four.
To sum it all up: With this understanding, if you create your artwork using 100% one color black text then only one plate is needed to reproduce the text portions of your printed job and the end result is crystal clear pure black text, even when your printed order contains other full color images such as graphics and photos.