Board Thread:Questions and Answers/@comment-15.211.153.76-20130416035328/@comment-5706972-20130416194058

As was said:

Forest only finds: red / yellow

Water only finds: blue / purple

Fire only finds: blue / turquoise

To get the other treasures and finish the set you need to attack players of the corresponding element.

PS: Check out my Noob Tips page if you haven't already.