RGB and CMYK are two different styles of color mixing and have their own uses.
RGB is the primary color display of digital devices and refers to three colors ( Red, Green, Blue ) that create a more vibrant color spectrum than CMYK. We recommend designing your artworks in RGB which is the native color setting in Photoshop. Bear in mind that without color correction, printed artworks designed in RGB will appear more subdued than compared to how they look on a display.
CMYK is a combination of the four ink pigment colors ( Cyan, Magenta, Yellow, and Black) that are layered together to create the various colors that go to print.
If possible, we would prefer the designs to be CMYK over RGB.