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"native-base": "^2.3.10",
"react": "16.2.0",
"react-native": "https://github.com/expo/react-native/archive/sdk-25.0.0.tar.gz",
borderBottomColor can be changed
borderBottomColor remained unchanged as default color
<Tab heading="Tab1"
tabStyle={styles.tabStyling}
activeTabStyle={styles.activeTabStyle}
textStyle={styles.tabTextStyle}
activeTextStyle={styles.activeTabTextStyle} />
const styles = StyleSheet.create({
tabStyling: {
backgroundColor: '#37b372'
},
activeTabStyle: {
backgroundColor: '#37b372',
borderColor: 'white',
opacity: 1000
},
tabTextStyle: {
color: 'black'
},
activeTabTextStyle: {
fontWeight: 'bold',
color: 'white',
fontSize: 20
}
});

@isaaclem Did you refer NativeBase Docs?
@isaaclem I find there is wrong usage of components
Please refer docs
To be honest @SupriyaKalghatgi it wasn't that easy to figure out. Had to do a bit of trial and error to figure out that it expects the 'backgroundColor' to change it and also on the Tabs instead of activeTabStyle
The solution for anyone hitting this page is:
You set the background color on Tabs with tabBarUnderlineStyle
<Tabs tabBarUnderlineStyle={{backgroundColor: "red"}}>