Michael Miller Jet black is very good and fabric fixer will probably be a good idea.

Color fasting wash- 1 cup vinegar, 1 cup salt, full load worth of a mild laundry soap color or luke warm water. Does 10 yards of fabric- dry on medium to high heat

I finally found a deep, dark black. It is True Black by Michael Miller.
You can get it on the Hancock's of Paducah website. If you purchase a bolt, you get a great discount. Before I sew the quilt,
I wash the black and all my other fabrics in hot water in the machine in retayne. It really works and keeps the blacks and all colors bright and deep. Retayne is available at your LQS or you can purchase it online at JoAnn.

Same here. Also, have you thought about a "khaki" color? I have found that it makes a good "blender" for sashing.

I am a hand dyer and Black and Navy are the hardest colors to dye. You need to use 4-6 times the dye and salt to increase the electron charge to make the dye bond to the fabric. I know most fabrics you will use will be "printed" but it is interesting I think that hand dyes have the same - if not worse - black fading issues.

Yes, if it is exposed to the light it will fade. I don't use black in my quilts very often.

I find that all patchwork (quilting) fabric fades which is very disappointing