RGB stands for the colours red, green, and blue, the colours widely recognised in design fields as the primary colours and which are used on monitors. The RGB model is known as an additive model.
CMYK stands for cyan, magenta, yellow, and black – the inks we use in print. CMYK is a subtractive model. This gets a bit complicated, but the idea with subtractive models like CMYK is that colours from the spectrum are subtracted from natural white light into pigments or dyes.
Typically, blue will look slightly more vibrant when displayed in RGB compared with CMYK. This means that if you create your design in RGB and print it in CMYK you’ll probably see a beautiful bright blue colour on the screen but on the printed version, it will appear like a purple-ish blue. The same is true for greens, they tend to look a little flat when converted to CMYK from RGB.
BEST to work in CMYK (if your application allows) when designing for print. PLUS ALWAYS HAVE A
PROOF BEFORE PRINTING – remember those vibrant colours on the screen will not always be the same when printed.