Except for the borders, the top is done!
I may need to sew some yellow cloth behind the yellow pieces, since they are somewhat translucent. Or maybe just having the white batting behind them will be enough. For this picture, the top was draped over a dark brown couch.
Assembling the large 3-triangle blocks was unexpectedly difficult. I had planned to just cut the pieces out with a quarter-inch seam allowance and sew them together, but on the rare times when I actually sewed the correct pieces together, they refused to come out correctly. Either the top and bottom edges were not parallel, or the piece was the wrong size, or (more commonly) both. I hadn't paper-pieced them because the pattern would have been 9 1/2 inches wide, and I didn't have a printer that wide. So, after struggling with one block for three hours, I posted a message on a couple of quilting groups on Yahoo titled "Pulling My Hair Out". Several responses suggested paper piecing. I remembered that we have a nice big printer at work that handles 11 x 17-inch paper. I made patterns, and pieced them with no further problem.
The only remaining problem happened when trying to assemble the middle and bottom strips. The inner corners did not meet. It turned out the center block on the bottom (blue and red triangles) was 9 3/8 inches wide instead of 9 1/2 inches. I was able to stretch it out by ironing, and got the seams to match.