Why do chinese people in hong kong treat south asians, people with darker skin, so rudely?

i have witnessed this myself, been subjected to it first hand, and have even heard about it from friends..My domestic helper from the Phillipines, has confided in me about what she has to endure in terms of racism in this city which professes to be a ' world city'..NOT used to be treated this way, i would really like to know where all this comes from..Once asked to clarify, very very politely, one item of billing in a restaurant i was taken aback when the owner told me to ''**** off, this is my pahlah!''..any explanations for the psychology for this behaviour?