This device-independent colorspace reference was developed by the International Commission on Illumination. The L channel represents lightness of color (0 is black, while 100 is diffuse white).
A represents positions between green and magenta, while B represents positions between blue and yellow, illustrated as follows:
LAB colorspace (Source: By Holger kkk Everding – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=38366968)
Apart from these three, there are various other color models in existence. For the purposes of our current use case around image colorization, we will take a rather interesting approach.