White screen before splash screen

Hi to everyone.
I have a “problem” with my app. When it’s running first time, before the splash screen and the app it’s ready, a white screen appears for about 5/6 seconds and it’s see run time media file permission alert box and after 5/6 second splash screen run.
How is it possible to avoid this white screen?

I didn’t saw a lot of question about this (without working answers) and I would like to have an updated answer

I don’t post code because I don’t know which code could be usefull.
use ionic 2

ionic (Ionic CLI) : 4.2.1 (/usr/lib/node_modules/ionic)
Ionic Framework : ionic-angular 3.9.2
@ionic/app-scripts : 3.1.2


cordova (Cordova CLI) : 8.0.0
Cordova Platforms : android 6.4.0, browser 5.0.4
Cordova Plugins : cordova-plugin-ionic-webview 1.1.1, (and 26 other plugins)


Android SDK Tools : 26.1.1 (/home/whitelotus/Android/Sdk)
NodeJS : v10.11.0 (/usr/bin/node)
npm : 4.6.1
OS : Linux 4.15

Thank you.