There are several ways of changing the color of an element.
Properties
Some UI elements have predefined style that you can apply using the property panel.
Usually, it’s the type property, but in the card widget, there is also the depth property.
Theme
You can update the theme of your project, all UI elements will be impacted.
Style
Lastly, you can update the style of the element.
You can either set an arbitrary color, or select a predefined color from the tokens. The latter is preferred.
You can change the background color, the font color, or the border color, for example.