How to use the angular-highcharts.Highcharts.Color function in angular-highcharts

versionsData = versionsData.concat(versions.map(function(v, index) {
                        var brightness = 0.2 - (index / versions.length) / 5;
                        return {
                            name: v.browser + ' ' + v.browserVersion,
                            y: toPercent(v.visits, totalVisits),
                            color: Highcharts.Color(color).brighten(brightness).get()
                        };
                    }));
                });