Before I painted it, I played around with some color mixing using my (VERY limited) assortment of watercolors. If there was one thing I remember from my college art instruction, it was the emphasis on getting darks by mixing complementary colors and avoiding black. I never really paid much attention to the siennas and umbers at all (remember - I tended toward the vibrant expressionist color palette back then).
I did have one instructor that required paintings done each week with limited color palettes (as dictated by him). I think it was a great exercise, HOWEVER there just wasn't time enough for me to really get into it and learn from it. I just always felt more focused on getting it done and moving on to the next thing.
Anyway, I have found that I LOVE umber - my new color friend. I love the earthiness it brings to colors - darkens them but keeps them warm (where black darkens but cools). I used both light and dark umber A LOT in the chicken drawing with colored pencil, and I used dark umber in many of the colors in today's painting.