Component.js

import { BLUE_COLOR } from './globalStyles';
import { styles } from './styles';

export default () => {
  return (
    <View style={styles.local}>
      <Text style={{ color: BLUE_COLOR }}>Hello World!</Text>
    </View>
  );
};

globalStyles.js

export const RED_COLOR = '#ff0000';
export const GREEN_COLOR = '#00ff00';
export const BLUE_COLOR = '#0000ff';

export const globalStyles = {
  global: {
    flex: 1,
    flexDirection: row,
    backgroundColor: RED_COLOR
  }
};

styles.js

import { globalStyles, BLUE_COLOR } from './globalStyles';
import Stylesheet from 'react-native';

export const styles = Stylesheet.create({
  local: {
    ...globalStyles.container,
    backgroundColor: GREEN_COLOR
  }
});