This one's pretty obvious.
I'm beginning to add more acrylic in again – the walls and the X, but I especially like the reflected blue light along the platypus' back. It's easy to get a range of color in the tone with watercolor, but to really make it pop, the acrylic is great.
I got the idea for the blue from J.C. Leyendecker's paintings. There's one where he has a painting of a man, and the highlight at the top of the sternum, just below the neck, is in that shade of blue. And it worked perfectly. Had it been just a shade of the color around it, it would have been flat and boring. So I'm going to try and bring more of that into these watercolors as well.