How to color space between two lines with a colour transition? - python-3.x

Question

How to colour space between two lines with a colour transition? For instance, with grey colour - the dark grey from the upper line should become lighter as proceeding to the lower line. Thank you
import matplotlib.pyplot as plt
import numpy as np
fig, ax = plt.subplots()
plt.rcParams["figure.figsize"] = [8, 8]
x = np.linspace(0, 1, 100)
y = 0.3*x
ax.set_ylim(-0.2, 0.6)
ax.plot(x, y)
width_l = ax.get_ylim()[1] - ax.get_ylim()[0]
ax.plot(x, y - 0.1*width_l)
plt.show()
Edit
And this, please? How to make the width of the coloured part the same?
import matplotlib.pyplot as plt
import numpy as np
import pywt
fig, ax = plt.subplots()
plt.rcParams["figure.figsize"] = [8, 8]
wavelet = pywt.ContinuousWavelet('morl')
psi, x = wavelet.wavefun(level=2)
cmap = plt.get_cmap('Greys_r')
ax.plot(x, psi)
ax.set_xlim(ax.get_xlim()[0], ax.get_xlim()[1])
y_a = ax.get_ylim()
ax.set_ylim(y_a[0],y_a[1]*1.3)
width_l = ax.get_ylim()[1] - ax.get_ylim()[0]
x_range = ax.get_xlim()[1] - ax.get_xlim()[0]
x_shift = x_range * 0.1
ax.plot([x[0]+x_shift, x[1]+x_shift], [psi[0], psi[1]])
ax.plot([x[2]-x_shift, x[3]-x_shift], [psi[2], psi[3]])
ax.plot([x[1], x[2]], [psi[1]-width_l*0.1, psi[2]-width_l*0.1])
for t in np.linspace(0, 1, 40):
ax.plot(x, psi - t * 0.1 * width_l, color=cmap(t/2 + 0.25))
plt.show()

Answer 1

You could draw a lot of parallel lines (or curves) using a color from a gray-scale colormap. The example code below uses a transformation u = t/2 + 0.25, so when t goes from 0 to 1, u would just go between 0.25 and 0.75 to select of specific range from the colormap, avoiding the very dark and very light parts.
import matplotlib.pyplot as plt
import numpy as np
fig, ax = plt.subplots()
plt.rcParams["figure.figsize"] = [8, 8]
x = np.linspace(0, 1, 100)
y = 0.3 * x
width_l = ax.get_ylim()[1] - ax.get_ylim()[0]
ax.set_ylim(-0.2, 0.6)
cmap = plt.get_cmap('Greys_r')
for t in np.linspace(0, 1, 40):
u = t/2 + 0.25
ax.plot(x, y - t * 0.1 * width_l, color=cmap(u))
ax.plot(x, y)
ax.plot(x, y - 0.1 * width_l)
plt.show()