A couple of people asked about the thread I used for my Watercolor Bars quilt. It's called Invisafil, and it's a very fine, 100- weight, polyester thread that creates a fine quilting line and blends pretty well into the fabric. I thought it was a wonderful alternative to monofilament. I'm sure it would work very well for applique too, either hand or machine applique.
If you google it, you may find some different places that sell it; but I got mine from Sharla Hicks' website here. I've shopped at her site before. She has quite a wide range of different products, and she ships pretty quickly. More than once I've found things at her site that I wasn't able to locate elsewhere. I think her prices are pretty good too. No affiliation.