title: How to change theme in native base?
body: <p>I'm currently new in react native and tried to use native base, the component is good but I'm in stuck to change the theme in native base while I know how to use style but not all of them can be applied in native base (such as change color in active footer tab). Even it can be customize in style I would prefer to change in theme just like in the doc. But I can't overcome this.</p>
  
  <p>I've tried to use my custom Themes and applied in my component so far but it didn't change. </p>
  
  <p>My Workspace:
  -react-native 2.0.1
  -native-base 2.3.1</p>
  
  <p>Thanks</p>