App.js

import React, { Component } from 'react';

import {
    View,
    Text,
    TouchableOpacity
} from 'react-native';

import ModalTester from './ModalTester.js';

export default class App extends Component {
    render () {
        return (
            <View style={{ flex: 1 }}>
              <TouchableOpacity onPress={() => this.Modal.showModal()}>
                <Text style={{color: 'black'}}>Mostrar</Text>
              </TouchableOpacity>
              <ModalTester ref={ref => this.Modal = ref}>
                <TouchableOpacity onPress={() => this.Modal.hideModal()}>
                  <Text style={{color: 'black'}}>Esconder</Text>
                </TouchableOpacity>
              </ModalTester>
            </View>
        );
    }

}

ModalTester.js

import React, { Component } from 'react';
import { Text, View, StyleSheet } from 'react-native';
import Modal from 'react-native-modal';

export default class ModalTester extends Component {
    state = {
        isModalVisible: false
    }

    showModal = () => this.setState({ isModalVisible: true })

    hideModal = () => this.setState({ isModalVisible: false })

    render () {
        return (
            <View style={{ flex: 1 }}>
              <Modal isVisible={this.state.isModalVisible}>
                {this.props.children}
              </Modal>
            </View>
        );
    }

}

import React, { Component } from 'react';
import { Image, StyleSheet, } from 'react-native';
import { Header, Container, Content, View, Card, CardItem, Icon, Thumbnail, Text, Button, Left, Body } from 'native-base';
import ModalTester from './../Cold/cold.js';
import Modal from 'react-native-modal';

export default class Form extends Component {

render() {
    return (


        <Container>
            <Content>
                <Header hasTabs >

                    <Button onPress={() => this.Modal.showModal()}>
                        <Text >Mostrar</Text>
                    </Button>
                </Header>


            </Content>
        </Container >
    );
}

}