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I open the polyplane emat under the trees mesh properties  and over on those  object properties or details tab...  under basic material modifiers you *could* play around with those values ( Diffuse IBL, Specular IBL,  Diffuse, Specular, etc  I was able to make a pine tree look purple...)    and change those colors.  

^^ this way might be much easier I realized without having to export and import stuff and using external applications to accomplish it etc.   Excuse my awful screenshot.      

The easiest way I can think of is by duplicating the asset and switching the parts its made of.
For example if I want to edit a tree i would duplicate it and then edit prefab:  
object properties > mesh object     >  Materials                        > here youll have things like "bark, polyplane, atlas" emat files, you could possibly copy one of those and replace it with something, but editing most likely would be best done with GIMP or something.                                                 > now for the polyplane you'll wanna duplicate that, and switch out the  file images like the BCR map, which you could also duplicate and export it to edit in photoshop/gimp to change the colors.       Might be an easier way but it's basically how ive done it with surface masks and vegetation so far.     Feel free to correct me. 

Alright, thanks for your help! ☺️

Thanks to BI for featuring the trailer in their community announcement few days ago.

So yeah, Yulakia is coming by the end of this month. We are still polishing some stuff and adding some requested features by testers... we have managed to connect the lake with underground river... and we went overboard with some of details and lost another week 😉 this project is taking a heavy toll... I hope it will be worth it to the best gaming Community since June 22, 2001.