Manual colorbar with range, shown as a small inset with label

colorbar.py

import matplotlib as mpl
import matplotlib.pyplot as plt

# make a colormap that can be used to look up colors
norm = mpl.colors.Normalize(vmin=0, vmax=3)
zcmap = plt.cm.ScalarMappable(norm=norm, cmap=plt.cm.viridis)

# use it to plot stuff
plt.errorbar(
    x=1, xerr=0.1, y=2, yerr=0.2,
    color=zcmap.to_rgba(redshifts[i]),
)

# show the color bar in the panel
cax = plt.axes([0.85, 0.5, 0.02, 0.2]) # left, bottom, width, height
cbar = plt.colorbar(zcmap, orientation="vertical", cax=cax)
cbar.set_label('redshift')