Simple put: HEX colors are good for displays, but you need the corresponding CMYK color value for printing (p.e. for Adobe InDesign). The color systems of HEX (Hexadecimal) and CMYK (Cyan, Magenta, Yellow and Black) are very different from each other. For instance, the HEX colors space contains more possible colors than the CMYK color space. This means that not every color looks the same on displays as they look if you print it out. If you need a lot of vibrant colors in your design and then convert them to cmyk, it often looks a lot less vibrant. This cannot be avoided, because like mentioned before, HEX can display a lot more colors than CMYK. If you want to print a vibrant color like red, blue or green for your design, especially if you want to print logos, consider using the PANTONE System, which supports a whole lot more colors than CMYK does. Most good Printing services can handle PANTONE colors. They really look amazing and are standardized worldwide.