There are two ways to customize colors on your website:
Global styles settings
Within the editor, expand the Styles panel on the left and open the Colors tab. Here, you'll find all colors that are used across your website. The most frequently used colors appear at the top of the list. Click Change next to any color, select a new one and it will replace the previous color all across your website:
Remember that you still can edit the appearance of individual elements and sections manually anytime (see below).
Local style settings
Click on a preferred element, select Edit and change its color individually. For example, click on a text element, and select Edit text. Then, select (highlight) a portion of text you'd like to change the color of and click on a color picker: