Bill

It really looks very much similar to the species you mentioned. We also have this plant with pink-flower-like leaves in many gardens in Hong Kong. I think those bouganvilla on wikipedia looks more beautiful.

Thank you very much!

I hope so, eula.
By the way, I think my spotting is probably small cabbage white instead of indian cabbage white as the species you suggested has black apexes with sawtooth-like edge which are absent from the species in the photo.
The two whites are very similar and common. The apexes would be the key to distinguish them. (2 more photos have been added)

Thank you, Eula.
I still have some more photos of butterflies and other organisms actually. And I'll post them here and in your mission later.
There're many HK people having better photos and interesting spottings, I believe they haven't spot this website yet!