Depending on the main purpose of your mixtape cover design, the color mode is either RGB or CMYK.
If you are designing your mixtape cover artwork to be used for print and phyical distribution, like at concerts or live shows, you should use the CMYK color mode. This format has less colors than RGB, but is a lot more accurate with the final product and required by all the professional mixtape printing companies. This means the final product will look the exact same as the graphic design you created.
If you are only placing your mixtape artwork online, to websites like DatPiff and LiveMixtapes or even iTunes, you should use the RGB color mode. This format has millions of more colors than CMYK, but it cannot be duplicated accurately with any printer.
The Mixtape Cover Store has multiple pre-designed Photoshop templates, created in CMYK color mode, to help you make a mixtape cover the right way. Each .PSD mock up template is available for free and as an instant download. Log on to the Mixtape Cover Store today and get your project started the right way.