How to change the navigation bar in React Native with a Modal?

I'm making a modal component to show when a user registers. But I have the following issue.

When I go to the register window, I can see the navigation bar in a blue color:

But when the modal is launched, the navigation bar color changes:

I change the navigation bar with this library in the App file:

And I've tryed to insert the changeNavigationNavbar function into the modal, but it doesn't works...

I would like to make it invisible. How can I make it?