@Max91
The Design Center does not provide an option for setting the status bar theme (yet).
The status bar theme/color is easy to manually configure by adding the following meta-tag to your webapp HTML
<meta name=”apple-mobile-web-app-status-bar-style” content=”black” />
content values: default, black, black-translucent
Note: that you should avoid modifying the mobione HTML UI code until your design is complete to avoid being overwritten by future design changes.