Open the App menu and chose System -> Settings -> Themes
Themes
With version 4 with have introduced a number of inbuilt colour themes for you to choose from or you can create your own custom theme. Choose your theme from the dropdown box.
If you choose to create a custom Theme then you will be able to select fonts, default colours, and other display options.
Chunk Sizes
The second tab gives you control of how your audio pane looks; change the size and spacing of your audio chunks and sections.