Black can be created by laying out multiple colors on top of each other, so instead of pure black being used, your screen and printer will register 100% black as an overlay first of CMY (cyan, magenta, and yellow) and finally, it will process K (black) over top the blend. This creates a lighter black resulting in transparency that is more like a dark gray when against bright colors.
If you choose to stick with CMYK coloring when doing a multi-color project including black, your best option from there is to create a rich black. This is created by altering the CMY colors to create a darker mix. The most common combination for a rich black that does not represent any other color would be a 60-40-40-100 CMYK.
100% Black v. Rich Black
In order to see how your colors are blending, especially in regards to any questions you have about a certain tone that appears, it is important to preview your separations. By previewing the separations before you print, you are able to view not only the blends that create your colors, but also where there may be any overprint within your design.
Once it comes to printing out your separations, it is highly recommended that you use RIP software. This will allow high-quality halftones creating a smoother and more vibrant blend. When choosing the ink to best represent your CMYK project, Union Tru-Tone Process Black will give you a consistent and accurate color reproduction.