I painted 99% of this using just two transparent colours: Raw Sienna and Raw Umber, plus a good deal of wiping back to board. The background, for example, was achieved by dabbing the paint on with tissues and fingers, waiting half an hour for it to tack up very slightly and then dabbing it back off again.
I used an oil primed linen board, as I couldn't do this on canvas or acrylic gesso. The paint would stain the surface too much, and you couldn't wipe back to white, or near white. I applied the paint in 3 or 4 layers waiting for each to dry and as I used W&N alkyd oils, applied very thinly, this did not take long.
At the very end I used Titanium White for her whiskers and the same, with a touch of Cad Lemon, for a few highlights.