For our milestone boards ($19.99), you can add a custom background!
To add a custom background to your milestone board, follow these steps:
1) Select Change Background (paintbrush icon) when viewing the board
2) In the pop-up panel select Custom background > click Add Custom Background
3) Select the header color you want and background color — or you can add an image (JPEG or PNG) for the background.
4) After you've added your custom background click Save Changes.
For an uploaded background image 2000 (w) x 1400 (l) or larger is optimal sizing.