Hello,
You can change the background color of the every button you have used in your project. To change the color of the button you have to follow these steps .
Select the "Button" option from the "ELEMENTS" -> Choose the button in which you want to add the custom color -> Click on "Background" -> Select "Normal" or "Hover"(as on effect you want to change the color) -> Select the color you want to add in that button background.