How to make a grey transit below the curve?

Hi, could I ask you for your help with the following script? How to edit the for cycles under #ax5 and #ax6 to plot graphs in the same fashion? Now, the lower figure has no colour transit, as opposed to the upper one. The colour transit appears in the lower figure after increasing of dpi, however, some unwanted stuff also appears. Is there a scaling problem? Thank you

``````import matplotlib.pyplot as plt
import numpy as np
from matplotlib.gridspec import GridSpec
import math

# Plot figure with size
fig, ax = plt.subplots()
plt.rcParams["figure.figsize"] = [8, 8]

def format_axes(fig):
for i, ax in enumerate(fig.axes):
ax.tick_params(labelbottom=False, labelleft=False)

for ax in [ax]:
ax.set_yticks([])
ax.set_xticks([])
# Removing axis
for side in ['right','top','left','bottom']:
ax.spines[side].set_visible(False)

# Function for plotting parallels to curves
def get_parallels(length=.1):

px, py = [], []

for idx in range(len(x)-1):
x0, y0, xa, ya = x[idx], y[idx], x[idx+1], y[idx+1]
dx, dy = xa-x0, ya-y0
norm = math.hypot(dx, dy) * 1/length
dx /= norm
dy /= norm
px.append(x0-dy)
py.append(y0+dx)
return px, py

def offset(x,y, o):
""" Offset coordinates given by array x,y by o """
X = np.c_[x,y].T
m = np.array([[0,-1],[1,0]])
R = np.zeros_like(X)
S = X[:,2:]-X[:,:-2]
R[:,1:-1] = np.dot(m, S)
R[:,0] = np.dot(m, X[:,1]-X[:,0])
R[:,-1] = np.dot(m, X[:,-1]-X[:,-2])
On = R/np.sqrt(R[0,:]**2+R[1,:]**2)*o
Out = On+X
return Out[0,:], Out[1,:]

dpi = 20

def offset_curve(ax, x,y, o):
""" Offset array x,y in data coordinates
by o in points """
trans = ax.transData.transform
inv = ax.transData.inverted().transform
X = np.c_[x,y]
Xt = trans(X)
xto, yto = offset(Xt[:,0],Xt[:,1],o*dpi/72. )
Xto = np.c_[xto, yto]
Xo = inv(Xto)
return Xo[:,0], Xo[:,1]

fig = plt.figure(constrained_layout=True)

gs = GridSpec(3, 6, figure=fig)

# Color map
cmap = plt.get_cmap('Greys_r')

# ax5
x = np.linspace(-1, 1, 100)
y = -x**2
ax5.set_ylim(-1.02, 0.3)
width_l = ax5.get_ylim()[1] - ax5.get_ylim()[0]
for t in np.linspace(0, 1, 40):
length =  -0.1*width_l*t
ax5.plot(*get_parallels(length=length), color=cmap(t/2 + 0.25))

# ax6
x = np.linspace(-3, 3, 100)
y = -(1/4*x**4 - 1.6*x**2)
ax6.plot(x, y)
ax6.set_xlim(ax6.get_xlim()[0]-0.5, ax6.get_xlim()[1]+0.5)
ax6.scatter(1/2*(ax6.get_xlim()[0] + ax6.get_xlim()[1]), 1.2, marker = 'o', s=900, facecolors='none')
lines = []
width_l = ax6.get_ylim()[1] - ax6.get_ylim()[0]
for t in np.linspace(0, 1, 40):
l, = ax6.plot(x, y - t * 0.1 * width_l, color=cmap(t/2 + 0.25))
lines.append(l)

def plot_rainbow(event=None):
x0 = x
y0 = y
for i in range(len(lines)):
xx, yy = offset_curve(ax, x0, y0, -width_l)
lines[i].set_data(xx, yy)
lines[i].set_linewidth(1.1*width_l)
x0 = xx
y0 = yy

plot_rainbow()
fig.canvas.mpl_connect("resize_event", plot_rainbow)
fig.canvas.mpl_connect("button_release_event", plot_rainbow)

# ax7
x = np.linspace(-3, 3, 100)
y = 1/4*x**4 - 1.6*x**2
ax7.plot(x, y)
ax7.set_ylim(ax7.get_ylim()[0]-1.5, ax7.get_ylim()[1])
ax7.set_xlim(ax7.get_xlim()[0]-0.5, ax7.get_xlim()[1]+0.5)
ax7.scatter(1/2*(ax7.get_xlim()[0] + ax7.get_xlim()[1]), 1.2, marker = 'o', s=900, facecolors='none')
width_l = ax7.get_ylim()[1] - ax7.get_ylim()[0]
lines = []
for t in np.linspace(0, 1, 40):
l, = ax7.plot(x, y - t * 0.1 * width_l, color=cmap(t/2 + 0.25))
lines.append(l)

plot_rainbow()
fig.canvas.mpl_connect("resize_event", plot_rainbow)
fig.canvas.mpl_connect("button_release_event", plot_rainbow)

format_axes(fig)

# Save the figure (.pdf)
plt.tight_layout()
plt.savefig('fig.pdf')
``````