PolyU has the best reputation for design related courses in Hong Kong.
I think the vocational training college ( vtc.edu.hk ) has some courses too.
Finally, you might want to check with the hong kong interior decorators association (
http://www.hkida.org/ ) for courses which might be suitable in English. While the curriculum is supposed to be taught in English -- most professors and students will slip into Cantonese on a frequent basis.