Matplotlib - Recreating stackplot gridlines rendering in plot with fill_between

I need to recreate a stackplot as a simple plot with fill_between (no stacking). The gridlines rendering appear to differ and I can't figure out how to make them look the same. Here's the code:

import pandas as pd
import numpy as np

mpl.rcParams.update(mpl.rcParamsDefault)
plt.style.use("ggplot")

_styles = {
'axes.edgecolor': '#bcbcbc',
'axes.facecolor': 'white',
'grid.color': '#b2b2b2',
'grid.linestyle': '--',
}

plt.rcParams.update(_styles)


def plot_a_plot(x_axis, actual, predicted, size=(10,4)):
    plt.figure(figsize=size)
    
    p1 = plt.plot(x_axis, actual, alpha=0.5, label=actual.name, lw=0.5)
    plt.fill_between(x_axis, actual.astype(np.float64), color='#F0A498', alpha=1, zorder=1)
    
    p2 = plt.plot(x_axis, predicted, alpha=0.5, label=predicted.name, lw=0.5)
    plt.fill_between(x_axis, predicted.astype(np.float64), color='C1', alpha=0.5, zorder=0)
    
    plt.grid(True, zorder=10)
    
    plt.title('Plot with fill_between')
    plt.show()

def plot_a_stackplot(x_axis, actual, predicted, size=(10,4)):
    y = np.vstack([actual.astype(float), predicted.astype(float)])
    plt.figure(figsize=size)
    plt.stackplot(x_axis, y, labels=[actual.name, predicted.name], alpha=0.5, edgecolors="face")
   
    plt.title('Stackplot')
    plt.show()

arr = np.random.rand(10)

data = {
  "actual": arr,
  "predicted": arr*2
}

df = pd.DataFrame(data)

x_axis = df.index
actual = df['actual']
predicted = df['predicted']

plot_a_plot(x_axis, actual, predicted)
plot_a_stackplot(x_axis, actual, predicted)

View example here

Changing zorder doesn't seem to have any effect, I also played with alpha levels etc - nothing seems to work. The gridlines on stackplot just look the way it's meant to look, and gridlines on simple plot look muddy.

It seems that zorder doesn't work well with the value 0. In this demo, it is always chosen >=1.
The gird will look the same as with stackplot if you change your function to:

def plot_a_plot(x_axis, actual, predicted, size=(10,4)):
    plt.figure(figsize=size)
    
    p1 = plt.plot(x_axis, actual, alpha=0.5, label=actual.name, lw=0.5)
    plt.fill_between(x_axis, actual.astype(np.float64), color='#F0A498', alpha=1, zorder=2)
    
    p2 = plt.plot(x_axis, predicted, alpha=0.5, label=predicted.name, lw=0.5)
    plt.fill_between(x_axis, predicted.astype(np.float64), color='C1', alpha=0.5, zorder=1)
    
    plt.grid(True, zorder=10)
    
    plt.title('Plot with fill_between')
    plt.show()

Edit: if you want the bottom area (red) to look exactly like with stackplot, you should use the right color. You can find out colors with:

for color in plt.rcParams['axes.prop_cycle']:
    print(color)

The first one is the one you're looking for: #E24A33 (C0 would work too)

From there, the second call on fill_between should fill between actual and predicted, otherwise the fill areas will overlap:

def plot_a_plot(x_axis, actual, predicted, size=(10,4)):
    plt.figure(figsize=size)
    
    p1 = plt.plot(x_axis, actual, alpha=0.5, label=actual.name, lw=0.5)
    plt.fill_between(x_axis, actual.astype(np.float64), color='#E24A33', alpha=0.5, zorder=2)
    
    p2 = plt.plot(x_axis, predicted, alpha=0.5, label=predicted.name, lw=0.5)
    plt.fill_between(x_axis, actual, predicted, color='C1', alpha=0.5, zorder=1)

    plt.grid(True, zorder=10)

    plt.title('Plot with fill_between')
    plt.show()