This is the appropriately named blue whistling thrush (Myophonus caeruleus).
Quite a shy bird, difficult to get close to, and it is a thrush that is found is normally found in the mountains. Here in Hong Kong we are lucky enough to see them for example in forests, often in stream beds, like here in Tai Po Kau. It is known for its loud human-like whistling song at dawn and dusk.
As you can see they are really dark violet blue with shiny spangling on the tips of the body feathers other than on the lores, abdomen and under the tail. Our word for the day: The lore (adj. loreal) is the region between the eyes and nostrils of birds, reptiles, and amphibians