Changing state of buttons after section is completed.

Hi everyone

I have tried everything on this thread regarding my programme and I cannot get it to do what I want. 

Essentially I have 6 sections that I want students to complete and after the last question in each section I want them to return to the master menu slide and the section button to become grey so they know they have completed that section. Once all 6 are grey I want then to take the students to an overall results slide (which I haven't made yet as I can't even do do the first bit!)

I have done the following:

- Created a variable named 'complete' and when the student clicks on a button it changes the state of the variable to true.

- Students then need to click the next button to go back to the master slide

- The section button has been set to change to a custom 'complete' state when the variable 'complete' is equal to true. 

However the section button is not greying out - so it's not changing state. 

I have attached my programme - I have only attempted to apply this on the Wrist section so far. Any fix I can then apply to the remaining 5 sections. 

Help would be greatly appreciated!

Emma