The main color of the series. In line type series it applies to the
line and the point markers unless otherwise specified. In bar type
series it applies to the bars unless a color is specified per point.
The default value is pulled from the options.colors
array.
In styled mode, the color can be defined by the
colorIndex option. Also, the series
color can be set with the .highcharts-series
,
.highcharts-color-{n}
, .highcharts-{type}-series
or
.highcharts-series-{n}
class, or individual classes given by the
className
option.