tone(tone) {
        let argb = this.cache.get(tone);
        if (argb === undefined) {
            argb = Hct.from(this.hue, this.chroma, tone).toInt();
            this.cache.set(tone, argb);
        }
        return argb;
    }
@param tone HCT tone, measured from 0 to 100.
@return ARGB representation of a color with that tone.