Ann asked recently: ” I’m thinking of breaking my addiction to burnt sienna, for example, seeing what Van Dyke brown and cadmium red would give me instead……Partly I have a lot of colours to use up that I’m not touching right now! All thoughts welcome.”
Extending your colour palette will, I’m sure, be exciting. You could start by just substituting another “red” for Burnt Sienna as you mention – try it and see…. I’ve done this regularly using Alizarin Crimson with Ultramarine Blue when I want a brighter-purpler effect. Whist you’re exploring this, the idea of painting with 2 colours, typically a warm and a cool, can lead to some interesting effects: Raw Sienna and Purple, Alizarin Crimson and Veridian, Alizarin Crimson with Ultramarine Blue, Yellow Ochre and Ultramarine Blue perhaps. With each combination, you will see that the work takes on a dramatically different “feel”.
One final thought would be to then add a little of the complement to the predominant tone in some of your highlights … that will pop!