There are a couple different crossover threads involved in the Stitchery Crossover technique.
The 12 weight cotton quilting thread (Spagetti by Wonderfil Specialty Threads) from your Mia Rosa (large spools) or Piazza (small spools) kit in two bright, contrasting colors.
Depending on which prerequisite course your started with, you should have enough of this tread to get started on this project. More is available HERE if you need it.
Used for basting, this thread is used to secure the quilt fabric to the stitchery fabric to and to mark where the stitchery ends and the quilt fabric border begins.
You may need a new spool of the 60-wt cotton sewing thread.
You have a spool of 60-wt thread in your Mia Rosa or Piazza kit that is perfectly usable for this project IF your quilt fabric is similar in color.
As a reminder, this thread is used to make the tiny stitches for applique - to secure the folded-under quilt fabric edge to the stitched piece.
For this step in the process, it's best to match the thread color to the quilt fabric.
Match the thread color to the quilt fabric that you have selected for your block(s).
In my case, I'm going to use the blue from the kit for the purple block version and a deep pink for the floral print blocks.
Go Dark or Go Gray
If you can't find an exact color match for your fabric, choose one a shade or two darker rather than a shade or two lighter.
For example, if your quilt fabric reads medium green. Your thread color choices could be a color a little bit darker or a little bit lighter than the fabric color. Choose the darker thread color for a more successful project.
When in doubt, try gray. Gray blends well across with nearly all fabrics
My favorite thread brand is Wonderfil. Their Efina thread line is a 60-wt cotton that comes in a variety of colors. It's not linty and it holds up well to stitching by hand. Efina is my first choice for the applique thread.
Shop for Efina (by Wonderfil) at your local independent quilt shop or online at Wonderfil.ca