Thanks Donna! I'm still trying to find where I found that comment about the horizon line (I have a feeling it was someone writing about Nicolas de Stael, or perhaps Joan Mitchell).
The other thing that I've been experimenting with recently is depth from colour. If you look at the work on a bright screen and let your eyes relax, you should be able to see the reds coming forward and the blues receding. This much has been known about for a long time (I got the idea from Klee's 1929 painting Fire in the Evening), but what I was trying to achieve here was to get more than two depth planes. I think having the green in the mix helps to create an intermediate depth layer, but that might just be my eyes. There's still so much we don't fully understand about colour perception, and I find it very exciting to explore this space.