Trees are white because they are birches, and birches are white. These are viewed in HLMV, so no big deal about lighting. Check Dux's new screenies of his map to see how they look ingame.
HERE
as for speedtree, yea ok its fun and easy to use, but doesnt work for Hl2 for many reasons and I just hate automatic stuff like Speedtree and AutoUV mapping, you totally loose the art behind modelling. What would you do if you add programs that made maps for ya?