Then I cut some more from my own (very small) cotton scrap bin, and Suzanne let me dig through her scraps for the rest, till I had 13 of each colour total. I added gray to make them into half-square triangles. Part of the reason this took so long to make was because I couldn't decide how to arrange the blocks. There are just too many options with half-square triangles! I debating doing a spiral, chevron, or random placement, but eventually came up with this off-centred diamond rainbow.
The quilting was easy enough - just straight-line echoes in the gray. For binding I debated several options, but anything with a colour in it made that colour in the rainbow jump out, and the same dark gray made the gray the focus. I settled on solid light gray and I think it's just perfect.
I love the awesome backing! I found this great cursive script numbers fabric at IKEA a while back and knew it had to be a quilt backing. Especially for $3.99/metre! If I recall correctly, it's called Nummer. Slightly thinner quality cotton, but just fine for a backing.
At about 52" x 64", it's a great length for one person (even a tall one!), or it's also good across two laps - just what we need for the couch.