For hiding mistakes, what works best is not only a thread color that blends in well with the fabric, but also a lighter weight thread. Aurifil 50wt 2-ply is a finer thread, as is Bottom Line (which is 60wt poly). Invisifil is also a possibility, as it blends with everything. The more contrast you have with thread color, and the heavier the weight of the thread, the more it will show.
If the thread you used in the samples is all standard thread, it is probably 50wt 3-ply. I personally don't use this type of thread for FMQ on my domestic machine anymore (used to) because I think it shows my mistakes more. With finer thread I look like a better quilter!
Edit: Other things I do routinely to minimize mistakes is use the same thread (including same color) in top and bobbin. When the thread is fine, this seems to help unify the quilting.
Last edited by Prism99; 02-25-2014 at 10:54 AM.