You make styles by editing the templates. The templates mostly contain HTML code, so if you know your HTML modifying the layout of the style will be easy.
For colors, you use the Style options. You use hex codes to call colors for background, category background etc.
If you don't know html, you can still do change colors, in vB2.
In vB3 you can do even more such as make the whole board a fixed width, get more detailed with colors. With simple CSS, which many people would supply for you, you can even set images as backgrounds of certain things with just one line of code.