lib/less/parser/parser.js
function () {
                    var rgb;

                    if (parserInput.currentChar() === '#' && (rgb = parserInput.$re(/^#([A-Fa-f0-9]{8}|[A-Fa-f0-9]{6}|[A-Fa-f0-9]{3,4})/))) {
                        return new(tree.Color)(rgb[1], undefined, rgb[0]);
                    }
                }
function () {
                    var rgb;

                    if (parserInput.currentChar() === '#' && (rgb = parserInput.$re(/^#([A-Fa-f0-9]{8}|[A-Fa-f0-9]{6}|[A-Fa-f0-9]{3,4})/))) {
                        return new(tree.Color)(rgb[1], undefined, rgb[0]);
                    }
                }
A Hexadecimal color  #4F3C2F  `rgb` and `hsl` colors are parsed through the `entities.call` parser.