The App Style page allows you to change the colour theme for your App. The settings in the App Style page are applied to all pages in the App.
Please be aware that if you use this option, the colour of the bottom tabs in your App will not change colour unless you change the 'tab type' from 'Custom Tabs' to 'Standard Tabs'. Note that 'Custome Tabs' are set by default across the App Wizard range of templates. The tab settings can be changed via the 'Navigation Settings' in the Application Dashboard.
For information on how to edit the tab settings go to Navigation Settings