Artificially accelerating the discolouration of leaves
The solution we used was unexpectedly simple, but not truly satisfactory:

We placed short branches with leaves in the freezer and took them out just two hours later. To my surprise, they already started to change color. 

They didn’t develop the deep reds they would normally have, but had a distinctive reddish hue. I suppose repeated freezing/thawing cycles could have improved the results, but the minor that was involved in project declared them “good enough”. For a conclusive answer, further experiments need to be done next summer.