For each Email Design template, you can configure the colour styles and backgrounds.
How to set the template colour styles
Click on Edit Styles (located just above the Saved Blocks section)
Click each drop down box to select your colours (you can also create a custom colour if you have your hex colour codes)
How to update an individual block's colour styles
To change the style of an individual block, hover your mouse over the block, click Style on that block, select your colours and click Save