如何根据条形图的x刻度改变条形图中条形的颜色？(Matplotlib，Python)

import matplotlib.pyplot as plt
import numpy as np

x = np.array(['A', 'B', 'C', 'D', 'E'])
y = np.array([10, 15, 7, 12, 9])

fig, ax = plt.subplots()
ax.bar(x, y, color='blue')  # 设置初始颜色为蓝色

def color_mapper(value):
    if value < 10:
        return 'red'  # 小于10的条形颜色为红色
    elif value >= 10 and value < 15:
        return 'yellow'  # 10到15之间的条形颜色为黄色
    else:
        return 'green'  # 大于等于15的条形颜色为绿色

for i, value in enumerate(y):
    color = color_mapper(value)
    ax.bar(x[i], value, color=color)

import matplotlib.pyplot as plt
import numpy as np

x = np.array(['A', 'B', 'C', 'D', 'E'])
y = np.array([10, 15, 7, 12, 9])

def color_mapper(value):
    if value < 10:
        return 'red'
    elif value >= 10 and value < 15:
        return 'yellow'
    else:
        return 'green'

fig, ax = plt.subplots()
ax.bar(x, y, color='blue')

for i, value in enumerate(y):
    color = color_mapper(value)
    ax.bar(x[i], value, color=color)

plt.show()