线性渐变:http://blog.csdn.net/u013808809/article/details/59634694

数据渐变: itemStyle        
填充区域渐变:areaStyle
itemStyle: { normal: { color: new echarts.graphic.LinearGradient(0, 0, 0, 1, [{ // 0% 处的颜色 offset: 0, color: 'red' }, { // 100% 处的颜色 offset: 1, color: 'blue' }], false) } },