I totally missed that before, but yes, they're different. If you're color correcting by the numbers in Photoshop, you absolutely must understand the difference. You use curves to color correct, and you change your numbers to CMYK to get the ratios right. That means you need to understand that you have blue/yellow, green/magenta, and red/cyan in your curves, otherwise you'll never get the numbers right. Or it'll at least take longer. Also, subtractive color is what your monitor displays: RGB. Additive is what you print: CMYK (K is key, or black). Most (photo) printers prefer RGB over CMYK. I believe their printers get confused if there's nothing to convert. Color spaces get far more specific than this. You have color gamuts, which are often referred to as color spaces. I work in ProPhoto, the largest gamut there is. sRGB is what jpeg is compatible with and generally what you see online. Adobe RGB is between sRGB and ProPhoto in range of colors. ColorMatch is similar to CMYK. And there are custom gamuts, such as the Costco one that I use quite often. That profile is designed specifically for one printer to give me the best results.
No worries, there was a second thread to this called " elements of design" but its since gone missing maybe a admin can restore it other wise i will have to find it on another forum i have posted it on in the past.
I didn't write this information, i used a source i found about 4 years ago when i was studying this and i was realativly new to the computer side of design. and i got premission to crop the information and edit it and images for a forum friendly ( interms of viewing ) version. Your all welcome.