Calculate difference in percentage between 2 hex colors

diff.ts

export function diff(color1: string, color2: string): number {
    if (!color1 && !color2) {
        return;
    }

    const _color1 = color1.charAt(0) == '#' ? color1.substring(1, 7) : color1;
    const _color2 = color2.charAt(0) == '#' ? color2.substring(1, 7) : color2;

    const rColor1 = parseInt(_color1.substring(0, 2), 16);
    const gColor1 = parseInt(_color1.substring(2, 4), 16);
    const bColor1 = parseInt(_color1.substring(4, 6), 16);

    const rColor2 = parseInt(_color2.substring(0, 2), 16);
    const gColor2 = parseInt(_color2.substring(2, 4), 16);
    const bColor2 = parseInt(_color2.substring(4, 6), 16);

    const p1color1 = rColor1 / 255 * 100;
    const p2color1 = gColor1 / 255 * 100;
    const p3color1 = bColor1 / 255 * 100;

    const p1color2 = rColor2 / 255 * 100;
    const p2color2 = gColor2 / 255 * 100;
    const p3color2 = bColor2 / 255 * 100;

    const perc1 = Math.round((p1color1 + p2color1 + p3color1) / 3);
    const perc2 = Math.round((p1color2 + p2color2 + p3color2) / 3);

    return Math.abs(perc1 - perc2);
}

example.ts

import { diff } from './diff'

diff('#ffffff', '#000000') // => 100
diff('#2d333d', '#000000') // => 21