问题描述：

有两个数据集：red wine数据集和white wine。我把它们组合在一起形成了wine_df。我想绘制它。我想给红色直方图绘制为红色，白色直方图绘制为白色。但对于某些直方图，其标签和颜色不一致。例如，第四个标签是（4，白色），而其颜色是红色。

import numpy as np
import pandas as pd
import matplotlib.pyplot as plt
import seaborn as sns

red_wine = pd.read_csv('https://raw.githubusercontent.com/nishanthgandhidoss/Wine-Quality/master/data/winequality-red.csv',
sep = ';')
white_wine = pd.read_csv('https://raw.githubusercontent.com/nishanthgandhidoss/Wine-Quality/master/data/winequality-white.csv',
sep = ';')

## Add a column to each data to identify the wine color
red_wine['color'] = 'red'
white_wine['color'] = 'white'

## Combine the two dataframes
wine_df = pd.concat([red_wine, white_wine])

colors = ['red','white']
plt.style.use('ggplot')
counts = wine_df.groupby(['quality', 'color']).count()['pH']
counts.plot(kind='bar', title='Counts by Wine Color and quality', color=colors, alpha=.7)
plt.xlabel('Quality and Color', fontsize=18)
plt.ylabel('Count', fontsize=18)
plt.show()

问题解决：

颜色是索引的级别，因此使用它来指定颜色。将代码行更改为：

counts.plot(kind='bar', title='Counts by Wine Color and quality', 
            color=counts.index.get_level_values(1), alpha=.7)

matplotlib可以将索引中的值解释为颜色。通常，您可以将唯一值映射到可识别的颜色，例如：

color = counts.index.get_level_values(1).map({'red': 'green', 'white': 'black'})