There may be something here.

Great! Thanks, that should be in there too. OTOH it doesn't discuss ListedColormap which is a great way to make concatenated colormaps, so I think that needs documenation as well. But thanks, I made an issue because I wanted to make sure folks pointed me to stuff I was missing!

I am not saying that the current doc is enough for every use case: TBH I never really understood it ^^.

... I understand it, but not well enough to not have to look it up everytime I need to make a colormap. Which is good, because it means I spend very little time making tweaked colormaps 😛

Looking at #7716 again, truncation is basically just e.g.

cmap = colors.ListedColormap(plt.cm.viridis(np.linspace(.3, .7, 256)))

and concatenation

cmap = colors.ListedColormap(np.vstack([
    plt.cm.viridis(np.linspace(0, .5, 50)),
    plt.cm.jet(np.linspace(.5, 1, 50)),
]))

with much more lines spent doing input checking/massaging than anything else, so I now agree that we may just want to better document this.
(This doesn't take care of over/under/bad, but neither does #7716...)

WRT https://matplotlib.org/gallery/images_contours_and_fields/custom_cmap.html, I took a crack at improving the explanation in #11905. If its actually better, I'd suggest we rewrite custom_cmap and also add a short ListedColormap example.