I know I build in black a lot. Most of my MOCs are in black, and generally I build other people's MOCs in black as well.
For me, I have a lot of black. Almost every set I have has tons of black liftarms, connectors, panels, etc. and less in other colours.
To a lesser extent, I guess it also looks pretty solid and holes are less noticeable. Perhaps that's just my own opinion
I am collecting lots of orange at the moment and thinking of starting a white collection too so maybe I'll be able to branch out a bit
In regard to my first point, I've noticed that lots of smaller sets contain very few coloured pieces. For example, the 42007 motorbike has a completely black/grey chassis and contains only 9 orange parts, yet the main colour is obviously orange. Perhaps that has something to do with it?