Cambiar color al boton de 'confirm location' en el mapa

screens/main/Map.js

@@ -111,7 +111,7 @@ export default function Map({route, navigation} ) {
           <Marker coordinate={pin1} />
         </MapView>
           <View style = {{position: 'absolute', bottom: '5%'}}>
-              <Button title= 'Confirm Location' onPress = {() => navigation.navigate('StateTime' , {Pin : pin1 , Appointment : Appointment, int_id : int_id, 
+              <Button title= 'Confirm Location' color = "#000000" onPress = {() => navigation.navigate('StateTime' , {Pin : pin1 , Appointment : Appointment, int_id : int_id, 
                 mapflag : mapflag, I_Token: i_token, U_Token: u_token
                 ,Username: username, I_Username: I_username})}/>
           </View>