Hi Lionhead - thanks for the AME screenshot.  That helps a great deal.  It looks to me as though you are trying to edit the color of the ground, rather than the foliage of the trees in your ecosystem.  You need to select the material for the leaves and edit that color instead.  You can find the tab to edit the leaves in the ecosystem in the 2nd tab in the World Browser:

 

I am no expert with Vue so if this doesn't do the trick, maybe someone else can lend a hand.