Printing in CMYK
I've designed my first business card and I'm trying to print it via Moo. I designed the card in Photoshop in RGB and Moo is requiring me to save in CMYK. CMYK does not support the colors I've chosen for my design. From what I've seen online there are no solutions or (acceptable) alternatives to this problem. It seems hard to believe that Moo is unable to print in the colors I've selected for my business card. Is there a way around this? What are my options?
There is no way to print RGB colors in CYMK simply because you can't 'print' RGB, as it's a projected light color space, not a reflective light (ie, ink) color space. Many colors overlap in RGB and CMYK spaces, but not all, as you've found out.
You can use spot colors to print more colors that CMYK can provide--which can get you closer to what you might want, but then you need to find a printer who can print in spot colors for you. I'm not sure if Moo offers that as an option.
Convert your art to CMYK and print it as-is.
Convert your art to CMYK, and manually adjust the values to increase their vibrancy. (RGB to CMYK conversion can make things look muddy, especially those bright blues). If you're in photoshop, you can try a few different Adjustment Layers to get the colors closer to where you want it. Color Balance and Levels would be a good place to start.
Places that accept RGB files online for print (many do), go through their own CMYK conversion process before sending something to press. At least if you manually tweak your colors, you'll have control over how your out-of-gamut values are handled.
Are your results going to look just like your RGB version? No. Some colors that you see on the screen just cannot be printed with CMYK ink.