Setting a background color for a box
Select the box whose color you want to change. To select multiple boxes, hold down Shift and click each box.
In the right panel, select the [Box] tab.
If the panel is closed, open the right panel.
In the [Appearance] menu, click the color swatch in the [Background Color] field to open the color palette.
How to use the color palette
The color palette lets you set colors in a variety of ways, including solid colors, gradients, RGBA/HEX code input, and a color picker.
For more details on how to use it, see Setting colors with the color palette.