Practice Painting Trees with Watercolor

Today I practiced painting trees.  I start by painting some light undertones where the dark areas will come through.  I've found that a light gray blue is good for this.  On top of that, I add some bright yellow for the highlights.  Then I start to layer on successively darker layers of green paint, being sure to pay attention to my light source.  To finish, I end with black to create some contrast and add additional value.  I don't know if there's a better way to do this - I only know what I've learned from watching youTube videos.  Anyway, here are what my trees are looking like at this point: