RGB will give you all colors. The best saturation in your colors comes from this mode. All web images are RGB (jpg or png) or indexed color (gif).
Because of the crossover back & forth from web to print, we have to deal with RGB (web) files and CMYK (print) files. If you try to put up a .jpg on the web that is CMYK, it won’t show up. It must be converted to RGB. CMYK images are used for print. If an RGB image slips past your print production, it can look awful and be a huge waste of printing dollars.
When I do any artwork, it all starts out in RGB. Images for color correction, vector logos, print ads, you name it. With proper use of the brand’s Pantone colors where applicable, I know that when I convert it to CMYK for print, it will experience a smaller amount of color change.
Once the artwork is finished and approved, the file is duplicated and print production is ran. This includes converting said print piece to CMYK and having a color proof printed to check color. Be sure to have a way to revert back to RGB if color tweaks are necessary (color correction is best done in RGB), but you have to print the proof in CMYK because that’s how printers are set up. Once your color is perfect, then move on to the rest of the print production with the CMYK file.
Why start out in RGB? Well, a couple reasons. One, is the crossover from web to print. When you convert an RGB file to CMYK, you loose color. RGB can make all colors. CMYK is limited to having 4 colors that have to make up thousands or millions of colors. So there is a compromise in the color to achieve an over all sense of all the desired colors. Two, RGB will always be more saturated, thus you want to preserve that. If you only have CMYK files of your artwork, you are missing out on the possible color you could have. CMYK files will be dulled and muted when compared to the vibrant colors that RGB can provide. This is where Pantone colors are best. Because of the change in color when converted to CMYK, Pantone allows you to see the colors as Spot colors (RGB) and how they will look once converted to 4C process (CMYK). Always pick colors with the least amount of variation for the best results.