I have 6 weights: two green, two red, and two white. In each pair one of the weights is heavier. All the heavy weights have the same weight, and all the light weights have the same weight. All the weights look identical apart from for colour.

I have a set of scales which I wish to use to find out which weights are the heavy weights. A weighing is a single use of the scales to weigh some of the weights against some others.

Clearly I can work out which three weights are the heavy ones using three weighings. (Why?)

Your challenge: using just two weighings, find a way to determine which weights are the heavy ones.