How to make a button change an object on a different page C#

Hi there, im developing an app with VS 2012 in C# and xaml

Basically my app is an app with lessons, and the lessons are seperated into different pages.

The easiest way for me to describe is this.

Menu with:

Lesson 1

Lesson 2

Lesson 3

Each lesson page has a button that goes to the next lesson, so if the user is on lesson 1 the next button will navigate straight to lesson 2 and so on. I want the button to change the properties on the button that navigates to lesson 1.

I understand how to change the properties of an object in C#, but I don't know how to call the button from a different page.

basicsBT.background = new SolidColorBrush(Windows.UI.Colors.Green);

is obviously how i'd change the background colour of the button. But I need the current page to be able to recognise the defined button.

If anyone can help it would be a big help, 

Thanks in advance.