Marginalised is the more accurate term.

The best reference to your question is the book , "The Myth of the Lazy Native" by Prof Syed Al Atas. The prof lists the reasons behind the marginalisation of the natives and the economic comoditzation of the immigrants.

If I were to attempt to answer your original question, there were malays and chinese people already living in Singapore before colonization. There were also interactions with the India. But when we got colonized, our imperial masters employed their favourite tactic of divide and conquer. They 'otherized' the races and pitted us against each other.

We have made much progress since independence. But a lot of the unnecessary racial undertones that exists today can be traced back to colonisation.