src/vs/base/common/color.ts/Color/getLighterColor
class Color:	static getLighterColor(of: Color, relative: Color, factor?: number): Color {
		if (of.isLighterThan(relative)) {
			return of;
		}
		factor = factor ? factor : 0.5;
		const lum1 = of.getRelativeLuminance();
		const lum2 = relative.getRelativeLuminance();
		factor = factor * (lum2 - lum1) / lum2;
		return of.lighten(factor);
	}