I have installed visual assist X, I use visual studio for my C++ development. However, I am not sure how can I enable the dark theme color scheme as mentioned here http://www.wholetomato.com/products/features/color.asp?
According to the documentation at the link, if you have a dark background and press the "use defaults" button, the colors will default to ones appropriate for a dark scheme:
The scheme selected upon installation or when pressing Use Defaults in the VA Options Dialog depends on your current IDE color scheme.