extensions/notebook-renderers/src/color.ts/Color/getRelativeLuminance
class Color:	getRelativeLuminance(): number {
		const R = Color._relativeLuminanceForComponent(this.rgba.r);
		const G = Color._relativeLuminanceForComponent(this.rgba.g);
		const B = Color._relativeLuminanceForComponent(this.rgba.b);
		const luminance = 0.2126 * R + 0.7152 * G + 0.0722 * B;

		return roundFloat(luminance, 4);
	}