Struggle is constant

I worked on the second layer of my coyote skull painting after a very full day. It continues to amaze me that I can have such good, flowy painting sessions, while others are a painful struggle through mud. And that mud is colours I've mixed. I'm working with warm greys because I'm trying to practice backlighting with an imaginary light source. I want the butterfly (on the skull) to feel like the light source so I have to imagine what the light pale green glow from the butterfly would look like. However, I can only backlight the skull with a candle which is warm lighting. Like I said, a struggle, but a rewarding one.