Colour Spaces: RGB, CMYK & Spot Colours
A colour space defines how colours are described and reproduced technically. Screens mix light additively in red, green and blue (RGB), four-colour printing mixes inks subtractively from cyan, magenta, yellow and black (CMYK), and spot colours are pre-mixed inks specified from a swatch system.
In practice
The practical point: not every screen colour can be printed. Strong blues and oranges glow on a monitor and look muted on paper; that is a property of the process, not a printer's error. So define separate values for every brand colour: a hex value for the web, a CMYK value for digital and offset printing, and where exactness matters, a spot colour for logo applications. sRGB is the default colour space of the web, defined in IEC 61966-2-1, and browsers assume it unless told otherwise. Before larger print runs, ask for a proof rather than trusting your own, usually uncalibrated, monitor.