You can customize the Webcamoid color theme going to Main menu/Preferences/Customize colors.

Here you can select between many available color schemes that fits your likes.

For creating new color schemes press Add, in the dialog you can set the color scheme name and set each element color. The new color scheme will take the current color scheme as reference.
You can also edit the current color scheme with Edit, which will show the same options. The color schemes provided by Webcamoid can't be edited or removed, but can be usedd as reference for creating new themes.
The System color scheme follows your current system color scheme.