Artificially accelerating the discolouration of leaves For a project I need leaves (apple, to be precise) that have turned into their fall colors. The leaves will be pressed later.

Is there a method that creates the color change within a day or two? Or at least a partial change?

I was thinking about placing a branch into the fridge over night and in lukewarm water / a sunny spot during the day. But that's just a stab in the dark based on what induces the change in nature.
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.