It used to work fine before (in Flex 2.0). Now with Flex 2.0.1, it renders as shown below when we define depthColors attribute for Tree Component
depthColors="[0xFFFFFF, 0xF2F6F7, 0xEDF5F7, 0xE8F0F2, 0xD3E2E6]"
If I find any workaround I will update this post. If you know a workaround please post it as a comment