Has there ever been a situation where the "motherland" treated its colonies well anywhere in the world?

Of course answering this question requires a lot of subjective judgments.

One interesting way that people have looked at this (which itself embeds a lot of partially-considered value judgments) is to compare different colonial regimes with each other on various dimensions.

The most prominent example of this approach that I know of is this paper by Acemogulu et al, which has come in for a ton of criticism but also inspired a lot more work.

I'm guessing there is more like this from before the latest "wave."

(h/t to Statsanalyst; the Acemoglu et al paper broadly agrees with his point that Britain seems to have been better)

Well, Spain founded many schools, hospitals and universities in their "colonies". The "New Laws" where approved a few years after the conquest of the Americas (1542) forbbiding the slavery and setting fair laws to protect the natives, officialy at least: https://en.wikipedia.org/wiki/New_Laws There was no official/legal discrimination agains specific races or ethnicities in New Spain territories, as stated by many authors: https://en.wikipedia.org/wiki/Casta#cite_note-1 Spaniards and natives mixed race during centuries and the "mestizos" were one of the dominant social statements. It could be discussed if what Spain did in their conquered territories could be called colonialism or not, actually.

I would recommend you to take a look at this good related answer from Lars: https://history.stackexchange.com/a/41974/40566

Of course there were often mistreatments, even more during the conquest times and wars, but overall I would say that this could be a fair example of what you were asking for.

After WW2 West-Germany and Japan were governed by the United States for a short time and thus were in essence colonies/protectorates during that period. I think most historians agree these countries were treated extremely well by their "master-country" during this period. Especially when you take into account the actions of these countries that resulted in them being protectorates.

The answer to this is, of course, a matter of opinion, rather than fact. However, in my view, the British Empire was largely a benevolent imperial power which generally treated the colonised nations/peoples exceptionally well, and was a tremendous force for good in the world. But many others would disagree. I would add that the French Empire was also a largely benevolent imperial power which arguably contributed to the progress of its colonised peoples.

Regarding the first sentence of your second paragraph, I would sound a note of caution. Every revolutionary government needs to justify the revolution ex post, which means that governments and the educational establishment have a very strong incentive to "teach" the next generation about the supposed horrors of the ancien regime. In the case of former colonies, this means ensuring that the next generation believes in the supposed evils of the colonial power (which are often exaggerated for this purpose), and that the benefits of the imperial era - education, healthcare, parliamentary democracy, a modern and objective legal system, etc - are downplayed. And historical support for the colonial power among the native population is ignored as a historical inconvenience. E.g. in Ireland, the fact that about 20% of the Irish population had been Unionists was very inconvenient for the post-revolutionary Irish government (and society), and so this was downplayed. The supposed (and, it has to be said, often real) crimes of the British authorities in Ireland were exaggerated, and Britain was made in 20th-century Irish historiography into an evil imperial power subjugating Ireland by force, with Irish Unionists portrayed as either Quisling-esque collaborationists or an elite governing class. The fact that many contemporary Irishmen regarded the revolutionaries of 1916 as extremists was also ignored for some time.

None of this is an attempt to justify the colonisation of Ireland - just an example of how historical nuance is lost in this, and many other cases, because post-revolution, it is necessary to create a historicistic narrative which justifies the revolution - partly because the authorities have an incentive to do so, and partly because the people of the country feel the need to.

So yeah, a long-winded way of saying, I wouldn't necessarily accept your schoolteachers' accounts of the evils of the French Empire without qualification, but take them with a pinch of salt. Consider at least that they may be either exaggerated, or else true, but selectively chosen.

Baltic states such as Estonia remember Swedish rule as the "good old [Swedish] times." That's because Swedish kings followed a policy of "reduction" that limited the power of nobles at home and abroad, thereby sparing the peasants from oppression more than German or Russian rulers.

Some of the UK colonies became independent on very friendly terms, and still maintain close ties to the UK. Canada, Australia, and New Zealand come to mind. However... their indigenous populations were pushed aside by the arriving colonists, so those people might feel otherwise about the experience.

Hong Kong didn't move from colony to self rule, it moved from colony of one nation to becoming part of a more authoritarian nation, with no real input from the HK residents on the transition.