As you may have pondered, color is such an inherently subjective thing. What exactly is blue - is it the color of a clear sky or the thick woven rug in the lounge room?
A color space is a way of quantifying colors. Different color spaces represent color in different ways.
This is not dissimilar to how the imperial system is a way to measure length in inches and the metric system deals with length in centimeters instead.
Some popular color spaces include RGB, CMYK and LAB.
What is the RGB color space?
The RGB color space describes color as a mixture of three fundamental colors - red, green and blue. This way, a color can be defined within a three dimensional space where red, green and blue are the axes.
RGB is a commonly used color space for screens, since the combination of red, green and blue inside a screen is what enables it to display the millions of colors that you see everyday.
You may be thinking... but what is red, green and blue in the first place? Its a great question. The reality is that there exists a variety of RGB 'flavours' which use different definitions of red, green and blue. These are known as RGB color profiles. More about RGB color profiles here.
What is the CMYK color space?
The CMYK color space describes color as a mixture of four fundamental colors - cyan, magenta, yellow and black.
CMYK is used very regularly in defining physical colors, particularly those produced by a printer. This is because cyan, magenta, yellow and black are the primary ink colors that combine to produce a desired color.
For the same reasons as the RGB space, CMYK also requires the use of a specific color profile to correctly define a color. After all, there are many ink colors which could rightly be called cyan, or magenta, or yellow, and even black! More about CMYK color profiles here.
What is the LAB color space?
The LAB color space describes color by its lightness ('L'), and hue (defined by 'a' and 'b').
A dark color will have a lower 'L' value. Very vibrant colors with high saturation will have very high or low 'a' and/or 'b' values.
In the LAB space, 'L' ranges from 0 (completely black) to 100 (completely white). But both 'a' and 'b' are unbounded and can be negative as well as positive. This means that any color observable can be given a LAB representation. This is in contrast with other color spaces (including RGB and CMYK) which have clear boundaries, and any colors outside of the boundary simply cannot be defined in those spaces.
In addition, because the definitions of 'L', 'a, and 'b' are fixed, the LAB space does not have specific profiles - it is just one space.
For the reasons above, the LAB space is regarded as a device-independent space, meaning that any color it represents does not depend on the fundamental colors or profiles used. Because of this, it is used as a standard when translating between color spaces, and for raw color measurements.