How do I Darken Foliage Color?

Hi. I’m trying to make the texture of the SpeedTree trees match up with those of the leaves in the foreground. Seems simple enough. But so far I’ve tried modifying the brightness and darkening the source texture in Gimp with no results. It looks dark enough in the material editor but in the actual scene it blends in poorly with the darker leaf texture in the foreground. Is this an issue with unbuilt lighting, perhaps?