My sister is the pro on hand embroidery (she goes everywhere with a project tucked in her purse--or at least some squares of muslin and a pencil to draw with and her needle/thread/thimble/snips). She has taught me that using a layer of muslin underneath (cheap is fine) keeps the under threads from showing through and is easier to needle and work with than a fusible. I have found that using red or black thread sometimes leaves color on the fabric just from using it--so do agree that using Retayne on the thread or finished blocks is important. Have fun!