That looks like fun! The whole cloth you posted earlier is gorgeous!
I did a similar peacock - wall hanging size (about 24 x 36 or so). I used a variegated rainbow machine embroidery thread that was a bit thick. (I think it was about 40wt or so). It came out all right, but I did it on a pale green background instead of white, and it wasn't as much contrast as I thought it would be.
I also did a goldfish (about 22" x 22" ) on a yellow background using shiny yellow machine embroidery thread. I liked the effect much better. But then I also went over it with a pearly fabric paint. I liked that effect ... or maybe just that process a bit better.
I also used 3 layers of batting on the fish, and got a 3D effect I didn't expect. I also traced my design on tracing paper, and then used it as a pattern....stitching right through the pattern, then removing the paper.
I first tried tracing the design on H2O soluble stabilizer. I used an H2O marker, but bits of that color stayed in the thread. Couldn't wash it out. Bummer.
Can't wait to see what you do with this design!
They are a bit spendy, but you might have fun with these (they are specifically made for thread painting:
https://www.superiorthreads.com/thre...-studio-colors