custom-tabbar-color.js

import React from 'react';
import { BottomTabBar } from 'react-navigation-tabs';

const TabBar = (props) => {
  const { navigation = {} } = props;
  const { state = {} } = navigation;
  
  let newProps = props;
  if (state.index === 0) {
    newProps = Object.assign(
      {},
      props,
      {
        style: {
          backgroundColor:"#000",
        },
        activeTintColor: '#fff',
        inactiveTintColor: '#bbb',
      },
    );
  }
  
  return <BottomTabBar {...newProps} />;
}

export default createBottomTabNavigator(
  RouteConfigs,
  {
    tabBarComponent: TabBar,
    tabBarPosition: 'bottom',
    animationEnabled: false,
    swipeEnabled: false,
  },
);

mongodb-promise.js

let nightMode = false;
(async () => {
  const dbCount = await new Promise(resolve => db.count({}).exec((error, docs) => {
    if (error) {
      return resolve(error);
    }

    return resolve(docs);
  }));

  console.log(dbCount)

  const response = await new Promise(resolve => db.findOne({}).exec((error, docs) => {
    if (error) {
      return resolve(error);
    }

    return resolve(docs);
  }));
  
  ...
  
  nightMode = true
})();

export const TabBar = (props) => {
  ...
  
  let newProps = props;
  if(nightMode){
    newProps = ...
  }
  
  return ...
}