function getLightness(rgbColor) {
	if (rgbColor[0] !== '#') {
		return 1.0; // Invalid color ?
	}
	rgbColor = rgbColor.slice(1);
	if (rgbColor.length === 3) {
		rgbColor = rgbColor[0] + rgbColor[0] +
			rgbColor[1] + rgbColor[1] + rgbColor[2] + rgbColor[2];
	}

	const hexColor = parseInt(rgbColor, 16);
	const r = hexColor >> 16;
	const g = hexColor >> 8 & 255;
	const b = hexColor & 255;
	const max = Math.max(r, g, b);
	const min = Math.min(r, g, b);

	return (max + min) / (2 * 255);
}
Creates a simple math expression using either the + or - operator
@param {number} [min] - The min value of the math expression defaults to 1
@param {number} [max] - The max value of the math expression defaults to 9
@param {string} [operator] - The operator(s) to use
@returns {{equation: string, text: string}}