Best to start with colours close to the base colour and then slowly move away in the colourspectrum.
Starting with a contrasting colour rarely ends up well without a lot of corrections and blending in.
If you do want to start with Burnt Umber, make sure you dilute it heavily. Better to apply 4 thin layers, than one too thick one that might ruin the effect. Also, with many thin layers, blending will be that much easier.
So in your case, I'd start with maybe a medium/dark olive colour (between brown and green) and move down (up?) to dark brown...