pyecharts桑基图节点颜色

要设置桑基图节点的颜色，可以在 `Sankey.add` 方法中通过参数 `node_color` 来指定节点的颜色。例如：

from pyecharts import options as opts
from pyecharts.charts import Sankey

nodes = [
    {"name": "A"},
    {"name": "B"},
    {"name": "C"},
    {"name": "D"},
    {"name": "E"}
]

links = [
    {"source": "A", "target": "B", "value": 10},
    {"source": "A", "target": "C", "value": 15},
    {"source": "B", "target": "D", "value": 12},
    {"source": "C", "target": "D", "value": 8},
    {"source": "D", "target": "E", "value": 20}
]

sankey = Sankey()
sankey.add(
    "sankey",
    nodes,
    links,
    node_gap=30,
    node_width=20,
    node_label_opts=opts.LabelOpts(position="right"),
    linestyle_opt=opts.LineStyleOpts(opacity=0.2),
    label_opts=opts.LabelOpts(font_size=14),
    node_color=["#FFB6C1", "#87CEFA", "#90EE90", "#FFC0CB", "#ADD8E6"]
)
sankey.render("sankey.html")

在 `node_color` 参数中传入一个列表，每个元素对应一个节点的颜色，节点的顺序与传入的 `nodes` 列表一致。