It's important to stay loose in your under painting it helps create the energy, brushwork and mood that you want to carry through the entire piece. The point of the under painting is to establish the compositional elements and the indicate the value relationships. If it's not working at this stage there's no point in going on. Plus the under painting feels very non-committal, not a lot of time or paint invested so it feels easier to make changes, even major ones at this point.
This is the second stage of the under painting. This is when I add ultramarine blue to get grays and to deepen values. I'm still not using any white at this point.
This is the first stage of adding color and developing detail. My palette is titanium white, hansa yellow, raw sienna dark, yellow ochre, sap green, napthol red, vermillion, transparent red oxide, ultramarine blue.
I've put in another couple of days work on this already and have made some compositional changes in the foreground and developed a lot of surface texture and richness. Should be done soon and I'll post a pic of the final version. Stay tuned!