When I began work on the structure, I used a purple grey that absolutely sang on the yellow canvas. Immediately, my grey painting had color. What a joy!
Here, the yellow underpainting still shows through quite a bit and I am working to match the chroma of it with greens at the bottom. The "grays" in the sky appear blue and purple.
In this last image, I've adjusted the movement of the blue grey in the middle of the composition, a very important element, and shifted it's location to the left in order to better balance the painting.
The painting at this stage still feels "yellow" but now the background color is more integrated into the heavier layers of paint. It shows through just a bit here and there in it's raw state, yet informs every color choice I have made.