How did natives get treated after imperialism in china?

Mostly as an inferior race. The British empire was especially "good" at this, mostly their armies who refused to believe that natives can put up a hell of a fight (Shaka Zulu and countless others proved them wrong). British had almost no appreciation for native cultures and exploited them, for example in India they used natives regardless of their caste system. That did not work well.

But the most outrageous exploitation was governed by Spanish empire. They discovered a moutain full of silver in Incan empire and they forced every native to work in mines for a given amount of time. But for refining silver they needed mercury, and they got it from other mines. Guess who had to work there? Guessed right. Mining silver is very dangerous because of poisonous dust and fumes. The conditions were so bad that some natives even resorted to maiming their children in order to spare them from it.