First let me start out by saying that Global process colors in Adobe Illustrator are mostly useful only if you’re doing a complex illustration or layout that uses a lot of the same color or tints of the same color. 
Global process colors are easily identified in Illustrator’s swatches palette by their empty white triangle in the lower right corner of the swatch. Spot colors use the same triangle, but put a small dot inside it, and process colors have no triangle at all. Global process colors allow you to create a single color swatch that you can update and have it apply, of course, globally. For instance, if you apply the same global color to many objects in your Illustrator document, then you decide you want to change the color, it only takes a click or two to update all the objects. You simply alter the global color to your liking, and everything on the page updates. You can create a Global process color by clicking the Global check box in the New Swatch dialog or the Swatch Options dialog box. Global colors are disabled by default.
