Why are CMYK and RGB colorspaces different and how are each used?
CMYK and RGB colorspaces (or modes) are distinct options that one can set when dealing with digital work, raster or vector-based. As CMYK is the color of inks used in the offset printing process and RGB is the color of an electronic display emitted from a computer, each colorspace has a specific use. CMYK is generally is used for producing photos and prints (where their colorspace can be easily manipulated by adjusting tones, contrast and mixing the color palette using software like Photoshop) while RGB is used for (vector-based) digital work, like in web design or in previewing a document or design project on screen prior to printing.
The specific reason for why CMYK and RGB are different is because each (while containing prominent colors of the color spectrum) uses color differently. One can still obtain yellow, for example, in both CMYK and RBG but they won’t be exact shades. RGB produces projective light and CMYK produces reflective light which respectively, means that they help make color sharply visible for viewing and dark enough where needed (to show color range) for printing.