Here's a color study and it's variations, with line, without line, with text, combined with the value study, etc. I will definitely exclude the line and use a painterly approach. I'm really enjoying the painting part of digital illustration. The colors are a complementary color palette of reds and greens with accents of golds. It seems to fit with the theme of Macbeth. Green is envy, red is seduction/murder/blood.
Value study and color study combined
Without the line looks best. It's softer and more sinister.