On the right hand side menu, there are colors editing tools which help you change both background colors as well as text colors. Some components have elements with own backgrounds already set. These will not be changed when you change the component background color.
Clicking on the Component Background button on the right hand side of the screen will reveal a color panel from where you can choose a color. Click on the color to apply it as a background for all the components.
All associated editors have a Text Color button with a similar behaviour to the Component Background. When clicking on the Text Color button, the same color panel appears. Clicking on a color will change the selected text color in the preview window. Reminder: The selected element is the element shown in the preview window, in the middle of the screen, with a red outline.