This is a very complicated question. First you have to understand that Indochina was made up of several people, it is not only one society. As its name indicates, these people are culturally either mainly under Chinese influence or under Indian influence. So just lumping them together as "Asians" might be a problem when talking about how the French treated them.

Anyway, the treatment of indigenous populations by the French was ambiguous. The French as in most colonies set up a local elite, particularly in what was to become Vietnam. What was to become the École nationale de la France d'outre-mer was founded in Paris by the colonial authorities to train high ranking khmer civil servants in 1889. Like in other French colonies the brightest students were often given the opportunity to come study in France (for instance Hồ Văn Nhựt studied in Paris, he would become an important political figure in South Vietnam, same for Bảo Đại, last emperor of Vietnam, or for Ngô Ðình Nhu, very important figure in South Vietnam).

There was no legal segregation but Indochinese were still considered as a lower class. For instance it was common for French men to have relationships (forced or consensual) with Indochinese women, but for a French woman to date an Indochinese man was seen as a transgression (Marguerite Duras, who lived in Indochina, wrote The Lover on this very topic). Another example of this is how the French were treated by the legal system in comparison with the Indochinese. It was common to get a lesser punishment for killing an Indochinese than for killing a European but this was not so much written into law as due to the general attitudes of colonial powers.

Persecution when it happened took place more on an economic plane. Indochina was never a population settlement, it was more of a resource colony. The French disturbed the Indochinese economy when they arrived. They took ownership of a lot of land, which led to a rise in the number of landless peasants which were often exploited by land-owners. In mines and factories corporal punishment was frequent and there was an obvious disparity in jobs and wages offered to Indochinese compared to that received by Whites. In that sense the local populations were largely exploited.

Finally, free, public schools were massively set up and the system ended up teaching up to a million children, mainly in what was to become Vietnam. But schools were also teaching a form of propaganda, and their installation disturbed the system of buddhist schools that was already set up, mostly in Cambodge.

The French population never went above 40,000 before the war and colonization was a widely debated topic in the mainland (socialist movements were getting stronger) which I think partially explains why there never was any attempts to despotically dominate the Indochinese.

EDIT: an interesting case of exploitation I forgot to mention is the forced labor of ~20,000 Indochinese who were deported to France at the beginning of WWII to work in the armament industry. Called the "Công Binh" they were pretty much not paid. After WWII their knowledge led to the creation of rice pads in France, which is why there are now sizable rice plantations in mainland France.

Well, look at it like this. There is no such thing as a humane colonial empire because colonialism is by definition violent and exploitative. It doesn't mean there aren't differences between empires or that colonial subjects sometimes weren't able to take advantage of colonial structures for their own benefit, or that there are many areas of ambiguous legacies left behind colonial rule. Even the problematic French film Indochine had a scene showing the common practice of French settlers whipping Vietnamese people.

Also violence can take many forms. You don't have to go around slaughtering people to be "violent."