Allowing learner to change background colour of slides

I am trying to add an accessibility function into courses by allowing learners to change the background colour of slides to suit their needs.

I have followed the posts on this, and have learnt how to do this by adding in the shapes and buttons to master slides. However, my question is, is there a way to do this so that the learner does not have to re-select their background colour on each slide?

I am finding that every time you move on through the course you have to re-select your background choice which could become frustrating.

Any help would be appreciated!